Develop Reference

Javascript - parse string to long

I have a working script in python doing string to integer conversion based on specified radix using long(16):
modulus=public_key["n"]
modulusDecoded = long(public_key["n"], 16)
which prints:
8079d7ae567dd2c02dadd1068843136314fa3893fa1fb1ab331682c6a85cad62b208d66c9974bbbb15d52676fd9907efb158c284e96f5c7a4914fd927b7326c40efa14922c68402d05ff53b0e4ccda90bbee5e6c473613e836e2c79da1072e366d0d50933327e77651b6984ddbac1fdecf1fd8fa17e0f0646af662a8065bd873
and
90218878289834622370514047239437874345637539049004160177768047103383444023879266805615186962965710608753937825108429415800005684101842952518531920633990402573136677611127418094912644368840442620417414685225340199872975797295511475162170060618806831021437109054760851445152320452665575790602072479287289305203
respectively.
This looks like a Hex to decimal conversion.
I tried to have the same result in JS but parseInt() and parseFloat() produce something completely different. On top of that JavaScript seems not to like chars in input string and sometimes returns NaN.
Could anyone please provide a function / guidance how to get the same functionality as in Python script?

Numbers in JavaScript are floating point so they always lose precision after a certain digit. To have unlimited numbers one could rather use an array of numbers from 0 to 9, which has an unlimited range. To do so based on the hex string input, i do a hex to int array conversion, then I use the double dabble algorithm to convert the array to BCD. That can be printed easily:
const hexToArray = arr => arr.split("").map(n => parseInt(n,16));
const doubleDabble = arr => {
var l = arr.length;
for( var b = l * 4; b--;){
//add && leftshift
const overflow = arr.reduceRight((carry,n,i) => {
//apply the >4 +3, then leftshift
var shifted = ((i < (arr.length - l ) && n>4)?n+3:n ) << 1;
//just take the right four bits and add the eventual carry value
arr[i] = (shifted & 0b1111) | carry;
//carry on
return shifted > 0b1111;
}, 0);
// we've exceeded the current array, lets extend it:
if(overflow) arr.unshift(overflow);
}
return arr.slice(0,-l);
};
const arr = hexToArray("8079d7");
const result = doubleDabble(arr);
console.log(result.join(""));
Try it

Using the built in api parseInt, you can get upto 100 digts of accuracy on Firefox and 20 digits of accuracy on Chrome.
a = parseInt('8079d7ae567dd2c02dadd1068843136314fa3893fa1fb1ab331682c6a85cad62b208d66c9974bbbb15d52676fd9907efb158c284e96f5c7a4914fd927b7326c40efa14922c68402d05ff53b0e4ccda90bbee5e6c473613e836e2c79da1072e366d0d50933327e77651b6984ddbac1fdecf1fd8fa17e0f0646af662a8065bd873', 16)
a.toPrecision(110)
> Uncaught RangeError: toPrecision() argument must be between 1 and 21
# Chrome
a.toPrecision(20)
"9.0218878289834615508e+307"
# Firefox
a.toPrecision(100)
"9.021887828983461550807409292694387726882781812072572899692574101215517323445643340153182035092932819e+307"
From the ECMAScript Spec,
Let p be ? ToInteger(precision).
...
If p < 1 or p > 100, throw a RangeError exception.

As described in this answer, JavaScript numbers cannot represent integers larger than 9.007199254740991e+15 without loss of precision.
Working with larger integers in JavaScript requires a BigInt library or other special-purpose code, and large integers will then usually be represented as strings or arrays.
Re-using code from this answer helps to convert the hexadecimal number representation
8079d7ae567dd2c02dadd1068843136314fa3893fa1fb1ab331682c6a85cad62b208d66c9974bbbb15d52676fd9907efb158c284e96f5c7a4914fd927b7326c40efa14922c68402d05ff53b0e4ccda90bbee5e6c473613e836e2c79da1072e366d0d50933327e77651b6984ddbac1fdecf1fd8fa17e0f0646af662a8065bd873
to its decimal representation
90218878289834622370514047239437874345637539049004160177768047103383444023879266805615186962965710608753937825108429415800005684101842952518531920633990402573136677611127418094912644368840442620417414685225340199872975797295511475162170060618806831021437109054760851445152320452665575790602072479287289305203
as demonstrated in the following snippet:
function parseBigInt(bigint, base) {
//convert bigint string to array of digit values
for (var values = [], i = 0; i < bigint.length; i++) {
values[i] = parseInt(bigint.charAt(i), base);
}
return values;
}
function formatBigInt(values, base) {
//convert array of digit values to bigint string
for (var bigint = '', i = 0; i < values.length; i++) {
bigint += values[i].toString(base);
}
return bigint;
}
function convertBase(bigint, inputBase, outputBase) {
//takes a bigint string and converts to different base
var inputValues = parseBigInt(bigint, inputBase),
outputValues = [], //output array, little-endian/lsd order
remainder,
len = inputValues.length,
pos = 0,
i;
while (pos < len) { //while digits left in input array
remainder = 0; //set remainder to 0
for (i = pos; i < len; i++) {
//long integer division of input values divided by output base
//remainder is added to output array
remainder = inputValues[i] + remainder * inputBase;
inputValues[i] = Math.floor(remainder / outputBase);
remainder -= inputValues[i] * outputBase;
if (inputValues[i] == 0 && i == pos) {
pos++;
}
}
outputValues.push(remainder);
}
outputValues.reverse(); //transform to big-endian/msd order
return formatBigInt(outputValues, outputBase);
}
var largeNumber =
'8079d7ae567dd2c02dadd1068843136314fa389'+
'3fa1fb1ab331682c6a85cad62b208d66c9974bb'+
'bb15d52676fd9907efb158c284e96f5c7a4914f'+
'd927b7326c40efa14922c68402d05ff53b0e4cc'+
'da90bbee5e6c473613e836e2c79da1072e366d0'+
'd50933327e77651b6984ddbac1fdecf1fd8fa17'+
'e0f0646af662a8065bd873';
//convert largeNumber from base 16 to base 10
var largeIntDecimal = convertBase(largeNumber, 16, 10);
//show decimal result in console:
console.log(largeIntDecimal);
//check that it matches the expected output:
console.log('Matches expected:',
largeIntDecimal === '90218878289834622370514047239437874345637539049'+
'0041601777680471033834440238792668056151869629657106087539378251084294158000056'+
'8410184295251853192063399040257313667761112741809491264436884044262041741468522'+
'5340199872975797295511475162170060618806831021437109054760851445152320452665575'+
'790602072479287289305203'
);
//check that conversion and back-conversion results in the original number
console.log('Converts back:',
convertBase(convertBase(largeNumber, 16, 10), 10, 16) === largeNumber
);

Having a hard time converting python to JS

I am trying to implement the math.frexp function in python. See here if you're confused. Apparently, I am working on this program on Khan Academy.
However, it is PJS and does not support DataView or ArrayBuffer. Can someone please help me with this implementation this?
Here is the current code (commented out because of DataView/ArrayBuffer). I found this on the Internet.
var frexp = function(value) {
if (value === 0){
return [value, 0];
}
var data = new DataView(new ArrayBuffer(8));//Does not support DataView and ArrayBuffer objects.
data.setFloat64(0, value);
var bits = (data.getUint32(0) >>> 20) & 0x7FF;
if (bits === 0) {
data.setFloat64(0, value * Math.pow(2, 64));
bits = ((data.getUint32(0) >>> 20) & 0x7FF) - 64;
}
var exponent = bits - 1022,
mantissa = value * Math.pow(2, -exponent);
return [mantissa, exponent];
};

It is not as efficient as reading the bytes
exponent = Math.trunc( 1023+Math.log( Math.abs(value) )/Math.LN2 ) - 1022;
mantissa = value * Math.pow(2,-exponent);
Should return a pair such that 2^(e-1) <= val < 2^e and thus 0.5 <= m < 1. In ECMA 6 the quotient can be replaced by Math.log2.
The floating point evaluation of the logarithm can lead to fuzzy results at dyadic powers. Which may give wrong results where e=exponent is one too small. Thus add the line
if (Math.abs(mantissa) >=1 ) { exponent +=1; mantissa /=2; }

How do I convert an integer to binary in JavaScript?

I’d like to see integers, positive or negative, in binary.
Rather like this question, but for JavaScript.

function dec2bin(dec) {
return (dec >>> 0).toString(2);
}
console.log(dec2bin(1)); // 1
console.log(dec2bin(-1)); // 11111111111111111111111111111111
console.log(dec2bin(256)); // 100000000
console.log(dec2bin(-256)); // 11111111111111111111111100000000
You can use Number.toString(2) function, but it has some problems when representing negative numbers. For example, (-1).toString(2) output is "-1".
To fix this issue, you can use the unsigned right shift bitwise operator (>>>) to coerce your number to an unsigned integer.
If you run (-1 >>> 0).toString(2) you will shift your number 0 bits to the right, which doesn't change the number itself but it will be represented as an unsigned integer. The code above will output "11111111111111111111111111111111" correctly.
This question has further explanation.
-3 >>> 0 (right logical shift) coerces its arguments to unsigned integers, which is why you get the 32-bit two's complement representation of -3.

Try
num.toString(2);
The 2 is the radix and can be any base between 2 and 36
source here
UPDATE:
This will only work for positive numbers, Javascript represents negative binary integers in two's-complement notation. I made this little function which should do the trick, I haven't tested it out properly:
function dec2Bin(dec)
{
if(dec >= 0) {
return dec.toString(2);
}
else {
/* Here you could represent the number in 2s compliment but this is not what
JS uses as its not sure how many bits are in your number range. There are
some suggestions https://stackoverflow.com/questions/10936600/javascript-decimal-to-binary-64-bit
*/
return (~dec).toString(2);
}
}
I had some help from here

A simple way is just...
Number(42).toString(2);
// "101010"

The binary in 'convert to binary' can refer to three main things. The positional number system, the binary representation in memory or 32bit bitstrings. (for 64bit bitstrings see Patrick Roberts' answer)
1. Number System
(123456).toString(2) will convert numbers to the base 2 positional numeral system. In this system negative numbers are written with minus signs just like in decimal.
2. Internal Representation
The internal representation of numbers is 64 bit floating point and some limitations are discussed in this answer. There is no easy way to create a bit-string representation of this in javascript nor access specific bits.
3. Masks & Bitwise Operators
MDN has a good overview of how bitwise operators work. Importantly:
Bitwise operators treat their operands as a sequence of 32 bits (zeros and ones)
Before operations are applied the 64 bit floating points numbers are cast to 32 bit signed integers. After they are converted back.
Here is the MDN example code for converting numbers into 32-bit strings.
function createBinaryString (nMask) {
// nMask must be between -2147483648 and 2147483647
for (var nFlag = 0, nShifted = nMask, sMask = ""; nFlag < 32;
nFlag++, sMask += String(nShifted >>> 31), nShifted <<= 1);
return sMask;
}
createBinaryString(0) //-> "00000000000000000000000000000000"
createBinaryString(123) //-> "00000000000000000000000001111011"
createBinaryString(-1) //-> "11111111111111111111111111111111"
createBinaryString(-1123456) //-> "11111111111011101101101110000000"
createBinaryString(0x7fffffff) //-> "01111111111111111111111111111111"

This answer attempts to address inputs with an absolute value in the range of 214748364810 (231) – 900719925474099110 (253-1).
In JavaScript, numbers are stored in 64-bit floating point representation, but bitwise operations coerce them to 32-bit integers in two's complement format, so any approach which uses bitwise operations restricts the range of output to -214748364810 (-231) – 214748364710 (231-1).
However, if bitwise operations are avoided and the 64-bit floating point representation is preserved by using only mathematical operations, we can reliably convert any safe integer to 64-bit two's complement binary notation by sign-extending the 53-bit twosComplement:
function toBinary (value) {
if (!Number.isSafeInteger(value)) {
throw new TypeError('value must be a safe integer');
}
const negative = value < 0;
const twosComplement = negative ? Number.MAX_SAFE_INTEGER + value + 1 : value;
const signExtend = negative ? '1' : '0';
return twosComplement.toString(2).padStart(53, '0').padStart(64, signExtend);
}
function format (value) {
console.log(value.toString().padStart(64));
console.log(value.toString(2).padStart(64));
console.log(toBinary(value));
}
format(8);
format(-8);
format(2**33-1);
format(-(2**33-1));
format(2**53-1);
format(-(2**53-1));
format(2**52);
format(-(2**52));
format(2**52+1);
format(-(2**52+1));
.as-console-wrapper{max-height:100%!important}
For older browsers, polyfills exist for the following functions and values:
Number.isSafeInteger()
Number.isInteger()
Number.MAX_SAFE_INTEGER
String.prototype.padStart()
As an added bonus, you can support any radix (2–36) if you perform the two's complement conversion for negative numbers in ⌈64 / log2(radix)⌉ digits by using BigInt:
function toRadix (value, radix) {
if (!Number.isSafeInteger(value)) {
throw new TypeError('value must be a safe integer');
}
const digits = Math.ceil(64 / Math.log2(radix));
const twosComplement = value < 0
? BigInt(radix) ** BigInt(digits) + BigInt(value)
: value;
return twosComplement.toString(radix).padStart(digits, '0');
}
console.log(toRadix(0xcba9876543210, 2));
console.log(toRadix(-0xcba9876543210, 2));
console.log(toRadix(0xcba9876543210, 16));
console.log(toRadix(-0xcba9876543210, 16));
console.log(toRadix(0x1032547698bac, 2));
console.log(toRadix(-0x1032547698bac, 2));
console.log(toRadix(0x1032547698bac, 16));
console.log(toRadix(-0x1032547698bac, 16));
.as-console-wrapper{max-height:100%!important}
If you are interested in my old answer that used an ArrayBuffer to create a union between a Float64Array and a Uint16Array, please refer to this answer's revision history.

A solution i'd go with that's fine for 32-bits, is the code the end of this answer, which is from developer.mozilla.org(MDN), but with some lines added for A)formatting and B)checking that the number is in range.
Some suggested x.toString(2) which doesn't work for negatives, it just sticks a minus sign in there for them, which is no good.
Fernando mentioned a simple solution of (x>>>0).toString(2); which is fine for negatives, but has a slight issue when x is positive. It has the output starting with 1, which for positive numbers isn't proper 2s complement.
Anybody that doesn't understand the fact of positive numbers starting with 0 and negative numbers with 1, in 2s complement, could check this SO QnA on 2s complement. What is “2's Complement”?
A solution could involve prepending a 0 for positive numbers, which I did in an earlier revision of this answer. And one could accept sometimes having a 33bit number, or one could make sure that the number to convert is within range -(2^31)<=x<2^31-1. So the number is always 32bits. But rather than do that, you can go with this solution on mozilla.org
Patrick's answer and code is long and apparently works for 64-bit, but had a bug that a commenter found, and the commenter fixed patrick's bug, but patrick has some "magic number" in his code that he didn't comment about and has forgotten about and patrick no longer fully understands his own code / why it works.
Annan had some incorrect and unclear terminology but mentioned a solution by developer.mozilla.org
Note- the old link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators now redirects elsewhere and doesn't have that content but the proper old link , which comes up when archive.org retrieves pages!, is available here https://web.archive.org/web/20150315015832/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators
The solution there works for 32-bit numbers.
The code is pretty compact, a function of three lines.
But I have added a regex to format the output in groups of 8 bits. Based on How to format a number with commas as thousands separators? (I just amended it from grouping it in 3s right to left and adding commas, to grouping in 8s right to left, and adding spaces)
And, while mozilla made a comment about the size of nMask(the number fed in)..that it has to be in range, they didn't test for or throw an error when the number is out of range, so i've added that.
I'm not sure why they named their parameter 'nMask' but i'll leave that as is.
https://web.archive.org/web/20150315015832/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators
function createBinaryString(nMask) {
// nMask must be between -2147483648 and 2147483647
if (nMask > 2**31-1)
throw "number too large. number shouldn't be > 2**31-1"; //added
if (nMask < -1*(2**31))
throw "number too far negative, number shouldn't be < -(2**31)" //added
for (var nFlag = 0, nShifted = nMask, sMask = ''; nFlag < 32;
nFlag++, sMask += String(nShifted >>> 31), nShifted <<= 1);
sMask=sMask.replace(/\B(?=(.{8})+(?!.))/g, " ") // added
return sMask;
}
console.log(createBinaryString(-1)) // "11111111 11111111 11111111 11111111"
console.log(createBinaryString(1024)) // "00000000 00000000 00000100 00000000"
console.log(createBinaryString(-2)) // "11111111 11111111 11111111 11111110"
console.log(createBinaryString(-1024)) // "11111111 11111111 11111100 00000000"
//added further console.log example
console.log(createBinaryString(2**31 -1)) //"01111111 11111111 11111111 11111111"

You can write your own function that returns an array of bits.
Example how to convert number to bits
Divisor| Dividend| bits/remainder
2 | 9 | 1
2 | 4 | 0
2 | 2 | 0
~ | 1 |~
example of above line: 2 * 4 = 8 and remainder is 1
so 9 = 1 0 0 1
function numToBit(num){
var number = num
var result = []
while(number >= 1 ){
result.unshift(Math.floor(number%2))
number = number/2
}
return result
}
Read remainders from bottom to top. Digit 1 in the middle to top.

This is how I manage to handle it:
const decbin = nbr => {
if(nbr < 0){
nbr = 0xFFFFFFFF + nbr + 1
}
return parseInt(nbr, 10).toString(2)
};
got it from this link: https://locutus.io/php/math/decbin/

we can also calculate the binary for positive or negative numbers as below:
function toBinary(n){
let binary = "";
if (n < 0) {
n = n >>> 0;
}
while(Math.ceil(n/2) > 0){
binary = n%2 + binary;
n = Math.floor(n/2);
}
return binary;
}
console.log(toBinary(7));
console.log(toBinary(-7));

You could use a recursive solution:
function intToBinary(number, res = "") {
if (number < 1)
if (res === "") return "0"
else
return res
else return intToBinary(Math.floor(number / 2), number % 2 + res)
}
console.log(intToBinary(12))
console.log(intToBinary(546))
console.log(intToBinary(0))
console.log(intToBinary(125))
Works only with positive numbers.

An actual solution that logic can be implemented by any programming language:
If you sure it is positive only:
var a = 0;
var n = 12; // your input
var m = 1;
while(n) {
a = a + n%2*m;
n = Math.floor(n/2);
m = m*10;
}
console.log(n, ':', a) // 12 : 1100
If can negative or positive -
(n >>> 0).toString(2)

I’d like to see integers, positive or negative, in binary.
This is an old question and I think there are very nice solutions here but there is no explanation about the use of these clever solutions.
First, we need to understand that a number can be positive or negative.
Also, JavaScript provides a MAX_SAFE_INTEGER constant that has a value of 9007199254740991. The reasoning behind that number is that JavaScript uses double-precision floating-point format numbers as specified in IEEE 754 and can only safely represent integers between -(2^53 - 1) and 2^53 - 1.
So, now we know the range where numbers are "safe". Also, JavaScript ES6 has the built-in method Number.isSafeInteger() to check if a number is a safe integer.
Logically, if we want to represent a number n as binary, this number needs a length of 53 bits, but for better presentation lets use 7 groups of 8 bits = 56 bits and fill the left side with 0 or 1 based on its sign using the padStart function.
Next, we need to handle positive and negative numbers: positive numbers will add 0s to the left while negative numbers will add 1s. Also, negative numbers will need a two's-complement representation. We can easily fix this by adding Number.MAX_SAFE_INTEGER + 1 to the number.
For example, we want to represent -3 as binary, lets assume that Number.MAX_SAFE_INTEGER is 00000000 11111111 (255) then Number.MAX_SAFE_INTEGER + 1 will be 00000001 00000000 (256). Now lets add the number Number.MAX_SAFE_INTEGER + 1 - 3 this will be 00000000 11111101 (253) but as we said we will fill with the left side with 1 like this 11111111 11111101 (-3), this represent -3 in binary.
Another algorithm will be we add 1 to the number and invert the sign like this -(-3 + 1) = 2 this will be 00000000 00000010 (2). Now we invert every bit like this 11111111 11111101 (-3) again we have a binary representation of -3.
Here we have a working snippet of these algos:
function dec2binA(n) {
if (!Number.isSafeInteger(n)) throw new TypeError('n value must be a safe integer')
if (n > 2**31) throw 'number too large. number should not be greater than 2**31'
if (n < -1*(2**31)) throw 'number too far negative, number should not be lesser than 2**31'
const bin = n < 0 ? Number.MAX_SAFE_INTEGER + 1 + n : n
const signBit = n < 0 ? '1' : '0'
return parseInt(bin, 10).toString(2)
.padStart(56, signBit)
.replace(/\B(?=(.{8})+(?!.))/g, ' ')
}
function dec2binB(n) {
if (!Number.isSafeInteger(n)) throw new TypeError('n value must be a safe integer')
if (n > 2**31) throw 'number too large. number should not be greater than 2**31'
if (n < -1*(2**31)) throw 'number too far negative, number should not be lesser than 2**31'
const bin = n < 0 ? -(1 + n) : n
const signBit = n < 0 ? '1' : '0'
return parseInt(bin, 10).toString(2)
.replace(/[01]/g, d => +!+d)
.padStart(56, signBit)
.replace(/\B(?=(.{8})+(?!.))/g, ' ')
}
const a = -805306368
console.log(a)
console.log('dec2binA:', dec2binA(a))
console.log('dec2binB:', dec2binB(a))
const b = -3
console.log(b)
console.log('dec2binA:', dec2binA(b))
console.log('dec2binB:', dec2binB(b))

One more alternative
const decToBin = dec => {
let bin = '';
let f = false;
while (!f) {
bin = bin + (dec % 2);
dec = Math.trunc(dec / 2);
if (dec === 0 ) f = true;
}
return bin.split("").reverse().join("");
}
console.log(decToBin(0));
console.log(decToBin(1));
console.log(decToBin(2));
console.log(decToBin(3));
console.log(decToBin(4));
console.log(decToBin(5));
console.log(decToBin(6));

I used a different approach to come up with something that does this. I've decided to not use this code in my project, but I thought I'd leave it somewhere relevant in case it is useful for someone.
Doesn't use bit-shifting or two's complement coercion.
You choose the number of bits that comes out (it checks for valid values of '8', '16', '32', but I suppose you could change that)
You choose whether to treat it as a signed or unsigned integer.
It will check for range issues given the combination of signed/unsigned and number of bits, though you'll want to improve the error handling.
It also has the "reverse" version of the function which converts the bits back to the int. You'll need that since there's probably nothing else that will interpret this output :D
function intToBitString(input, size, unsigned) {
if ([8, 16, 32].indexOf(size) == -1) {
throw "invalid params";
}
var min = unsigned ? 0 : - (2 ** size / 2);
var limit = unsigned ? 2 ** size : 2 ** size / 2;
if (!Number.isInteger(input) || input < min || input >= limit) {
throw "out of range or not an int";
}
if (!unsigned) {
input += limit;
}
var binary = input.toString(2).replace(/^-/, '');
return binary.padStart(size, '0');
}
function bitStringToInt(input, size, unsigned) {
if ([8, 16, 32].indexOf(size) == -1) {
throw "invalid params";
}
input = parseInt(input, 2);
if (!unsigned) {
input -= 2 ** size / 2;
}
return input;
}
// EXAMPLES
var res;
console.log("(uint8)10");
res = intToBitString(10, 8, true);
console.log("intToBitString(res, 8, true)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 8, true));
console.log("---");
console.log("(uint8)127");
res = intToBitString(127, 8, true);
console.log("intToBitString(res, 8, true)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 8, true));
console.log("---");
console.log("(int8)127");
res = intToBitString(127, 8, false);
console.log("intToBitString(res, 8, false)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 8, false));
console.log("---");
console.log("(int8)-128");
res = intToBitString(-128, 8, false);
console.log("intToBitString(res, 8, true)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 8, true));
console.log("---");
console.log("(uint16)5000");
res = intToBitString(5000, 16, true);
console.log("intToBitString(res, 16, true)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 16, true));
console.log("---");
console.log("(uint32)5000");
res = intToBitString(5000, 32, true);
console.log("intToBitString(res, 32, true)");
console.log(res);
console.log("reverse:", bitStringToInt(res, 32, true));
console.log("---");

This is a method that I use. It's a very fast and concise method that works for whole numbers.
If you want, this method also works with BigInts. You just have to change each 1 to 1n.
// Assuming {num} is a whole number
function toBin(num){
let str = "";
do {
str = `${num & 1}${str}`;
num >>= 1;
} while(num);
return str
}
Explanation
This method, in a way, goes through all the bits of the number as if it's already a binary number.
It starts with an empty string, and then it prepends the last bit. num & 1 will return the last bit of the number (1 or 0). num >>= 1 then removes the last bit and makes the second-to-last bit the new last bit. The process is repeated until all the bits have been read.
Of course, this is an extreme simplification of what's actually going on. But this is how I generalize it.

This is my code:
var x = prompt("enter number", "7");
var i = 0;
var binaryvar = " ";
function add(n) {
if (n == 0) {
binaryvar = "0" + binaryvar;
}
else {
binaryvar = "1" + binaryvar;
}
}
function binary() {
while (i < 1) {
if (x == 1) {
add(1);
document.write(binaryvar);
break;
}
else {
if (x % 2 == 0) {
x = x / 2;
add(0);
}
else {
x = (x - 1) / 2;
add(1);
}
}
}
}
binary();

This is the solution . Its quite simple as a matter of fact
function binaries(num1){
var str = num1.toString(2)
return(console.log('The binary form of ' + num1 + ' is: ' + str))
}
binaries(3
)
/*
According to MDN, Number.prototype.toString() overrides
Object.prototype.toString() with the useful distinction that you can
pass in a single integer argument. This argument is an optional radix,
numbers 2 to 36 allowed.So in the example above, we’re passing in 2 to
get a string representation of the binary for the base 10 number 100,
i.e. 1100100.
*/

How do I get the decimal places of a floating point number in Javascript?

What I would like to have is the almost opposite of Number.prototype.toPrecision(), meaning that when i have number, how many decimals does it have? E.g.
(12.3456).getDecimals() // 4

For anyone wondering how to do this faster (without converting to string), here's a solution:
function precision(a) {
var e = 1;
while (Math.round(a * e) / e !== a) e *= 10;
return Math.log(e) / Math.LN10;
}
Edit: a more complete solution with edge cases covered:
function precision(a) {
if (!isFinite(a)) return 0;
var e = 1, p = 0;
while (Math.round(a * e) / e !== a) { e *= 10; p++; }
return p;
}

One possible solution (depends on the application):
var precision = (12.3456 + "").split(".")[1].length;

If by "precision" you mean "decimal places", then that's impossible because floats are binary. They don't have decimal places, and most values that have a small number of decimal places have recurring digits in binary, and when they're translated back to decimal that doesn't necessarily yield the original decimal number.
Any code that works with the "decimal places" of a float is liable to produce unexpected results on some numbers.

There is no native function to determine the number of decimals. What you can do is convert the number to string and then count the offset off the decimal delimiter .:
Number.prototype.getPrecision = function() {
var s = this + "",
d = s.indexOf('.') + 1;
return !d ? 0 : s.length - d;
};
(123).getPrecision() === 0;
(123.0).getPrecision() === 0;
(123.12345).getPrecision() === 5;
(1e3).getPrecision() === 0;
(1e-3).getPrecision() === 3;
But it's in the nature of floats to fool you. 1 may just as well be represented by 0.00000000989 or something. I'm not sure how well the above actually performs in real life applications.

Basing on #blackpla9ue comment and considering numbers exponential format:
function getPrecision (num) {
var numAsStr = num.toFixed(10); //number can be presented in exponential format, avoid it
numAsStr = numAsStr.replace(/0+$/g, '');
var precision = String(numAsStr).replace('.', '').length - num.toFixed().length;
return precision;
}
getPrecision(12.3456); //4
getPrecision(120.30003300000); //6, trailing zeros are truncated
getPrecision(15); //0
getPrecision(120.000)) //0
getPrecision(0.0000005); //7
getPrecision(-0.01)) //2

Try the following
function countDecimalPlaces(number) {
var str = "" + number;
var index = str.indexOf('.');
if (index >= 0) {
return str.length - index - 1;
} else {
return 0;
}
}

Based on #boolean_Type's method of handling exponents, but avoiding the regex:
function getPrecision (value) {
if (!isFinite(value)) { return 0; }
const [int, float = ''] = Number(value).toFixed(12).split('.');
let precision = float.length;
while (float[precision - 1] === '0' && precision >= 0) precision--;
return precision;
}

Here are a couple of examples, one that uses a library (BigNumber.js), and another that doesn't use a library. Assume you want to check that a given input number (inputNumber) has an amount of decimal places that is less than or equal to a maximum amount of decimal places (tokenDecimals).
With BigNumber.js
import BigNumber from 'bignumber.js'; // ES6
// const BigNumber = require('bignumber.js').default; // CommonJS
const tokenDecimals = 18;
const inputNumber = 0.000000000000000001;
// Convert to BigNumber
const inputNumberBn = new BigNumber(inputNumber);
// BigNumber.js API Docs: http://mikemcl.github.io/bignumber.js/#dp
console.log(`Invalid?: ${inputNumberBn.dp() > tokenDecimals}`);
Without BigNumber.js
function getPrecision(numberAsString) {
var n = numberAsString.toString().split('.');
return n.length > 1
? n[1].length
: 0;
}
const tokenDecimals = 18;
const inputNumber = 0.000000000000000001;
// Conversion of number to string returns scientific conversion
// So obtain the decimal places from the scientific notation value
const inputNumberDecimalPlaces = inputNumber.toString().split('-')[1];
// Use `toFixed` to convert the number to a string without it being
// in scientific notation and with the correct number decimal places
const inputNumberAsString = inputNumber.toFixed(inputNumberDecimalPlaces);
// Check if inputNumber is invalid due to having more decimal places
// than the permitted decimal places of the token
console.log(`Invalid?: ${getPrecision(inputNumberAsString) > tokenDecimals}`);

Assuming number is valid.
let number = 0.999;
let noOfPlaces = number.includes(".") //includes or contains
? number.toString().split(".").pop().length
: 0;

5622890.31 ops/s (91.58% slower):
function precision (n) {
return (n.toString().split('.')[1] || '').length
}
precision(1.0123456789)
33004904.53 ops/s (50.58% slower):
function precision (n) {
let e = 1
let p = 0
while(Math.round(n * e) / e !== n) {
e *= 10
p++
}
return p
}
precision(1.0123456789)
62610550.04 ops/s (6.25% slower):
function precision (n) {
let cur = n
let p = 0
while(!Number.isInteger(cur)) {
cur *= 10
p++
}
return p
}
precision(1.0123456789)
66786361.47 ops/s (fastest):
function precision (n) {
let cur = n
let p = 0
while(Math.floor(cur) !== cur) {
cur *= 10
p++
}
return p
}
precision(1.0123456789)

Here is a simple solution
First of all, if you pass a simple float value as 12.1234 then most of the below/above logics may work but if you pass a value as 12.12340, then it may exclude a count of 0. For e.g, if the value is 12.12340 then it may give you a result of 4 instead of 5. As per your problem statement, if you ask javascript to split and count your float value into 2 integers then it won't include trailing 0s of it.
Let's satisfy our requirement here with a trick ;)
In the below function you need to pass a value in string format and it will do your work
function getPrecision(value){
a = value.toString()
console.log('a ->',a)
b = a.split('.')
console.log('b->',b)
return b[1].length
getPrecision('12.12340') // Call a function
For an example, run the below logic
value = '12.12340'
a = value.toString()
b = a.split('.')
console.log('count of trailing decimals->',b[1].length)
That's it! It will give you the exact count for normal float values as well as the float values with trailing 0s!
Thank you!

This answer adds to Mourner's accepted solution by making the function more robust. As noted by many, floating point precision makes such a function unreliable. For example, precision(0.1+0.2) yields 17 rather than 1 (this might be computer specific, but for this example see https://jsfiddle.net/s0v17jby/5/).
IMHO, there are two ways around this: 1. either properly define a decimal type, using e.g. https://github.com/MikeMcl/decimal.js/, or 2. define an acceptable precision level which is both OK for your use case and not a problem for the js Number representation (8 bytes can safely represent a total of 16 digits AFAICT). For the latter workaround, one can write a more robust variant of the proposed function:
const MAX_DECIMAL_PRECISION = 9; /* must be <= 15 */
const maxDecimalPrecisionFloat = 10**MAX_DECIMAL_PRECISION;
function precisionRobust(a) {
if (!isFinite(a)) return 0;
var e = 1, p = 0;
while ( ++p<=MAX_DECIMAL_PRECISION && Math.round( ( Math.round(a * e) / e - a ) * maxDecimalPrecisionFloat ) !== 0) e *= 10;
return p-1;
}
In the above example, the maximum precision of 9 means this accepts up to 6 digits before the decimal point and 9 after (so this would work for numbers less than one million and with a maximum of 9 decimal points). If your use-case numbers are smaller then you can choose to make this precision even greater (but with a maximum of 15). It turns out that, for calculating precision, this function seems to do OK on larger numbers as well (though that would no longer be the case if we were, say, adding two rounded numbers within the precisionRobust function).
Finally, since we now know the maximum useable precision, we can further avoid infinite loops (which I have not been able to replicate but which still seem to cause problems for some).

JavaScript summing large integers

In JavaScript I would like to create the binary hash of a large boolean array (54 elements) with the following method:
function bhash(arr) {
for (var i = 0, L = arr.length, sum = 0; i < L; sum += Math.pow(2,i)*arr[i++]);
return sum;
}
In short: it creates the smallest integer to store an array of booleans in. Now my problem is that javascript apparently uses floats as default. The maximum number I have to create is 2^54-1 but once javascript reaches 2^53 it starts doing weird things:
9007199254740992+1 = 9007199254740994
Is there any way of using integers instead of floats in javascript? Or large integer summations?

JavaScript uses floating point internally.
What is JavaScript's highest integer value that a number can go to without losing precision?
In other words you can't use more than 53 bits. In some implementations you may be limited to 31.
Try storing the bits in more than one variable, use a string, or get a bignum library, or if you only need to deal with integers, a biginteger library.

BigInt is being added as a native feature of JavaScript.
typeof 123;
// → 'number'
typeof 123n;
// → 'bigint'
Example:
const max = BigInt(Number.MAX_SAFE_INTEGER);
const two = 2n;
const result = max + two;
console.log(result);
// → '9007199254740993'

javascript now has experimental support for BigInt.
At the time of writing only chrome supports this.
caniuse has no entry yet.
BigInt can be either used with a constructor, e.g. BigInt(20) or by appending n, e.g. 20n
Example:
const max = Number.MAX_SAFE_INTEGER;
console.log('javascript Number limit reached', max + 1 === max + 2) // true;
console.log('javascript BigInt limit reached', BigInt(max) + 1n === BigInt(max) + 2n); // false

No. Javascript only has one numeric type. You've to code yourself or use a large integer library (and you cannot even overload arithmetic operators).
Update
This was true in 2010... now (2019) a BigInt library is being standardized and will most probably soon arrive natively in Javascript and it will be the second numeric type present (there are typed arrays, but - at least formally - values extracted from them are still double-precision floating point numbers).

Another implementation of large integer arithmetic (also using BigInt.js) is available at www.javascripter.net/math/calculators/100digitbigintcalculator.htm. Supports the operations + - * / as well as remainder, GCD, LCM, factorial, primality test, next prime, previous prime.

So while attempting one of the leetcode problem I have written a function which takes two numbers in form of string and returns the sum of those numbers in form of string.
(This doesn't work with negative numbers though we can modify this function to cover that)
var addTwoStr = function (s1, s2) {
s1 = s1.split("").reverse().join("")
s2 = s2.split("").reverse().join("")
var carry = 0, rS = '', x = null
if (s1.length > s2.length) {
for (let i = 0; i < s1.length; i++) {
let s = s1[i]
if (i < s2.length) {
x = Number(s) + Number(s2[i]) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
if (carry) {
x = Number(s) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
rS += s
}
}
}
} else {
for (let i = 0; i < s2.length; i++) {
let s = s2[i]
if (i < s1.length) {
x = Number(s) + Number(s1[i]) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
if (carry) {
x = Number(s) + carry
rS += String((x % 10))
carry = parseInt(x/10)
} else {
rS += s
}
}
}
}
if (carry) {
rS += String(carry)
}
return rS.split("").reverse().join("")
}
Example: addTwoStr('120354566', '321442535')
Output: "441797101"

There are various BigInteger Javascript libraries that you can find through googling. e.g. http://www.leemon.com/crypto/BigInt.html

Here's (yet another) wrapper around Leemon Baird's BigInt.js
It is used in this online demo of a big integer calculator in JavaScript which implements the usual four operations + - * /, the modulus (%), and four builtin functions : the square root (sqrt), the power (pow), the recursive factorial (fact) and a memoizing Fibonacci (fibo).

You're probably running into a byte length limit on your system. I'd take the array of booleans, convert it to an array of binary digits ([true, false, true] => [1,0,1]), then join this array into a string "101", then use parseInt('101',2), and you'll have your answer.

/** --if you want to show a big int as your wish use install and require this module
* By using 'big-integer' module is easier to use and handling the big int numbers than regular javascript
* https://www.npmjs.com/package/big-integer
*/
let bigInt = require('big-integer');
//variable: get_bigInt
let get_bigInt = bigInt("999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999");
let arr = [1, 100000, 21, 30, 4, BigInt(999999999999), get_bigInt.value];
console.log(arr[6]); // Output: 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999n
//Calculation
console.log(arr[6] + 1n); // +1
console.log(arr[6] + 100n); // +100
console.log(arr[6] - 1n); // -1
console.log(arr[6] - 10245n); // -1000n
console.log((arr[6] * 10000n) + 145n - 435n);