Related
Splitting a JavaScript string into "characters" can be done trivially but there are problems if you care about Unicode (and you should care about Unicode).
JavaScript natively treats characters as 16-bit entities (UCS-2 or UTF-16) but this does not allow for Unicode characters outside the BMP (Basic Multilingual Plane).
To deal with Unicode characters beyond the BMP, JavaScript must take into account "surrogate pairs", which it does not do natively.
I'm looking for how to split a js string by codepoint, whether the codepoints require one or two JavaScript "characters" (code units).
Depending on your needs, splitting by codepoint might not be enough, and you might want to split by "grapheme cluster", where a cluster is a base codepoint followed by all its non-spacing modifier codepoints, such as combining accents and diacritics.
For the purposes of this question I do not require splitting by grapheme cluster.
#bobince's answer has (luckily) become a bit dated; you can now simply use
var chars = Array.from( text )
to obtain a list of single-codepoint strings which does respect astral / 32bit / surrogate Unicode characters.
Along the lines of #John Frazer's answer, one can use this even succincter form of string iteration:
const chars = [...text]
e.g., with:
const text = 'A\uD835\uDC68B\uD835\uDC69C\uD835\uDC6A'
const chars = [...text] // ["A", "𝑨", "B", "𝑩", "C", "𝑪"]
In ECMAScript 6 you'll be able to use a string as an iterator to get code points, or you could search a string for /./ug, or you could call getCodePointAt(i) repeatedly.
Unfortunately for..of syntax and regexp flags can't be polyfilled and calling a polyfilled getCodePoint() would be super slow (O(n²)), so we can't realistically use this approach for a while yet.
So doing it the manual way:
String.prototype.toCodePoints= function() {
chars = [];
for (var i= 0; i<this.length; i++) {
var c1= this.charCodeAt(i);
if (c1>=0xD800 && c1<0xDC00 && i+1<this.length) {
var c2= this.charCodeAt(i+1);
if (c2>=0xDC00 && c2<0xE000) {
chars.push(0x10000 + ((c1-0xD800)<<10) + (c2-0xDC00));
i++;
continue;
}
}
chars.push(c1);
}
return chars;
}
For the inverse to this see https://stackoverflow.com/a/3759300/18936
Another method using codePointAt:
String.prototype.toCodePoints = function () {
var arCP = [];
for (var i = 0; i < this.length; i += 1) {
var cP = this.codePointAt(i);
arCP.push(cP);
if (cP >= 0x10000) {
i += 1;
}
}
return arCP;
}
Testing Hex Character Codes
Problem
What does a Vertical Tab or a Backspace character actually do? I want to find out.
My experiment is to find out exactly what happens when every hex character is put into a string. I thought the best way to do this would be to created a nested loop to go through each of the 16 hexadecimal characters to create each possible 2 digit hex character code.
I soon discovered that you cannot use the \x escape character with interpolated variables, and so I expect what I have set out to do might be impossible.
const hexCharacters = "0123456789ABCDEF";
let code = "";
let char1 = "";
let char2 = "";
for (charPos1 = 0; charPos1 < hexCharacters.length; charPos1++) {
for (charPos2 = 0; charPos2 < hexCharacters.length; charPos2++) {
char1 = hexCharacters[charPos1];
char2 = hexCharacters[charPos2];
code = `${char1}${char2}`;
printHexChar(code);
}
}
function printHexChar(string) {
let output = `<p>Hex Code ${string} = \x${string}</p>`; // THE PROBLEM IS CLEAR
document.write(output)
}
I know it will also probably fail once it gets past 7F or whichever is the last character in the set, but that's not the main issue here! :D
Potential solution
string.prototype.fromCharCode
This sort of string method approach would seem to be the answer, but it is meant for U-16 character codes, and that is not what I wanted to test. There doesn't seem to be an existing string method for hex codes. Probably because nobody would ever want one, but nevertheless it would be cool.
Conclusion
Is there any way to create an escape character sequence from assembled parts that will render not as plain text, but as a proper escape character sequence?
Apologies if this has been asked before in some form, but with my feeble understanding of things I just couldn't find an answer.
You can use String.fromCharCode with parseInt.
`<p>Hex Code ${string} = ${String.fromCharCode(parseInt(string, 16))}</p>`;
const hexCharacters = "0123456789ABCDEF";
let code = "";
let char1 = "";
let char2 = "";
for (charPos1 = 0; charPos1 < hexCharacters.length; charPos1++) {
for (charPos2 = 0; charPos2 < hexCharacters.length; charPos2++) {
char1 = hexCharacters[charPos1];
char2 = hexCharacters[charPos2];
code = `${char1}${char2}`;
printHexChar(code);
}
}
function printHexChar(string) {
let output = `<p>Hex Code ${string} = ${String.fromCharCode(parseInt(string, 16))}</p>`;
document.write(output)
}
eval works as well, though it should generally be avoided.
`<p>Hex Code ${string} = ${eval('"\\x'+string+'"')}</p>`
If you want to output \x literally, then in a string literal you need to escape the escape character, so `\\x`.
string.prototype.fromCharCode [...] is meant for U-16 character codes
JavaScript uses one character encoding. The following strings are all equal:
let a = String.fromCharCode(27);
let b = "\x1B";
let c = "\u001B";
console.log(a === b, b === c);
If I understand correctly, you want to produce a string literal that shows \x escape sequences -- not the actual character:
// Prepare string
let chars = Array.from({length: 128}, (_, i) => String.fromCharCode(i))
.join("");
// Escape them
let escaped = Array.from(chars, ch => `\\x${ch.charCodeAt().toString(16).padStart(2, "0")}`).join("");
console.log(escaped);
But you might also use JSON.stringify. Although it uses different escape sequences (\u instead of \x), and only for non-display characters, it will be the exact same string when evaluated. Here is a demo:
// Prepare string
let chars = Array.from({length: 128}, (_, i) => String.fromCharCode(i))
.join("");
// Escape them
let escaped = '"' + Array.from(chars, ch => `\\x${ch.charCodeAt().toString(16).padStart(2, "0")}`).join("") + '"';
console.log(escaped);
// Or JSONify them
let json = JSON.stringify(chars);
console.log(json);
// Compare them, when evaluated:
console.log(eval(escaped) === eval(json));
Finally, note that there is nothing special about hexadecimal: it is just a representation of an integer. In the end, it is the numerical value that is important, not the representation of it. It is that numerical value that corresponds to a character.
Addendum
If you prefer code that sticks to old-style JavaScript, here is something equivalent of the last code snippet:
// Prepare string
let chars = "";
for (let i = 0; i < 128; i++) {
chars += String.fromCharCode(i);
}
// Escape the characters in this string
let escaped = '"';
for (let i = 0; i < chars.length; i++) {
let ch = chars.charCodeAt(i);
let hex = ch.toString(16);
if (hex.length === 1) hex = "0" + hex;
escaped += "\\x" + hex;
}
escaped += '"';
console.log(escaped);
// Or JSONify them
let json = JSON.stringify(chars);
console.log(json);
// Compare them, when evaluated:
console.log(eval(escaped) === eval(json));
I am creating a script of time calculation from MySQL as I don't want to load the scripts on server-side with PHP.
I am getting the data and parsing it using JSON, which gives me a string of values for column and row data. The format of this data looks like:
1548145153,1548145165,End,Day;1548145209,1548145215,End,Day;1548148072,1548148086,End,Day;1548161279,1548161294,End,Day;1548145161,1548145163,End,Day;1548148082,1548148083,End,Day;1548161291,1548161293,End,Day
I need to split this string by semi-colon, and then extract the first VARCHAR number from before each comma to use that in subsequent calculation.
So for example, I would like to extract the following from the data above:
[1548145153, 1548145209, 1548148072, 1548161279, 1548145161, 1548148082, 1548161291]
I used the following type of for-loop but is not working as I wanted to:
for (var i=0; i < words.length; i++) {
var1 = words[i];
console.log(var1);
}
The string and the for-loop together are like following:
var processData = function(data) {
for(var a = 0; a < data.length; a++) {
var obj = data[a];
var str= obj.report // something like 1548145153,1548145165,End,Day;1548145209,1548145215,End,Day;1548148072,1548148086,End,Day;1548161279,1548161294,End,Day;1548145161,1548145163,End,Day;1548148082,1548148083,End,Day;1548161291,1548161293,End,Day
words = str.split(',');
words = str.split(';');
for (var i=0; i < words.length; i++) {
var1 = words[i];
var2 = var1[0];
console.log(var2);
}
Here is an approach based on a regular expression:
const str = "1548145153,1548145165,End,Day;1548145209,1548145215,End,Day;1548148072,1548148086,End,Day;1548161279,1548161294,End,Day;1548145161,1548145163,End,Day;1548148082,1548148083,End,Day;1548161291,1548161293,End,Day";
const ids = str.match(/(?<=;)(\d+)|(^\d+(?=,))/gi)
console.log(ids)
The general idea here is to classify the first VARCHAR value as either:
a number sequence directly preceded by a ; character (see 1 below) or, for the edge case
the very first number sequence of the input string directly followed by a , character (see 2 below).
These two cases are expressed as follows:
Match any number sequence that is preceded by a ; using the negated lookbehind rule: (?<=;)(\d+), where ; is the character that must follow a number sequence \d+ to be a match
Match any number sequence that is the first number sequence of the input string, and that has a , directly following it using the lookahead rule (^\d+(?=,)), where \d+ is the number sequence and , is the character that must directly follow that number sequence to be a match
These building blocks 1 and 2 are combined using the | operator to achieve the final result
First thing is that you override words with the content of str.split(';'), so it won't hold what you expect. To split the string into chunks, split by ; first, then iterate over the resulting array and within the loop, split by ,.
const str= "1548145153,1548145165,End,Day;1548145209,1548145215,End,Day;1548148072,1548148086,End,Day;1548161279,1548161294,End,Day;1548145161,1548145163,End,Day;1548148082,1548148083,End,Day;1548161291,1548161293,End,Day";
const lines = str.split(';');
lines.forEach(line => {
const parts = line.split(',');
console.log(parts[0]);
});
What you are doing is not correct, you'll have to separate strings twice as there are two separators. i.e. a comma and a semicolon.
I think you need a nested loop for that.
var str = "1548145153,1548145165,End,Day;1548145209,1548145215,End,Day;1548148072,1548148086,End,Day;1548161279,1548161294,End,Day;1548145161,1548145163,End,Day;1548148082,1548148083,End,Day;1548161291,1548161293,End,Day"
let words = str.split(';');
for (var i=0; i < words.length; i++) {
let varChars = words[i].split(',');
for (var j=0; j < varChars.length; i++)
console.log(varChars[j]);
}
I hope this helps. Please don't forget to mark the answer.
Splitting a JavaScript string into "characters" can be done trivially but there are problems if you care about Unicode (and you should care about Unicode).
JavaScript natively treats characters as 16-bit entities (UCS-2 or UTF-16) but this does not allow for Unicode characters outside the BMP (Basic Multilingual Plane).
To deal with Unicode characters beyond the BMP, JavaScript must take into account "surrogate pairs", which it does not do natively.
I'm looking for how to split a js string by codepoint, whether the codepoints require one or two JavaScript "characters" (code units).
Depending on your needs, splitting by codepoint might not be enough, and you might want to split by "grapheme cluster", where a cluster is a base codepoint followed by all its non-spacing modifier codepoints, such as combining accents and diacritics.
For the purposes of this question I do not require splitting by grapheme cluster.
#bobince's answer has (luckily) become a bit dated; you can now simply use
var chars = Array.from( text )
to obtain a list of single-codepoint strings which does respect astral / 32bit / surrogate Unicode characters.
Along the lines of #John Frazer's answer, one can use this even succincter form of string iteration:
const chars = [...text]
e.g., with:
const text = 'A\uD835\uDC68B\uD835\uDC69C\uD835\uDC6A'
const chars = [...text] // ["A", "𝑨", "B", "𝑩", "C", "𝑪"]
In ECMAScript 6 you'll be able to use a string as an iterator to get code points, or you could search a string for /./ug, or you could call getCodePointAt(i) repeatedly.
Unfortunately for..of syntax and regexp flags can't be polyfilled and calling a polyfilled getCodePoint() would be super slow (O(n²)), so we can't realistically use this approach for a while yet.
So doing it the manual way:
String.prototype.toCodePoints= function() {
chars = [];
for (var i= 0; i<this.length; i++) {
var c1= this.charCodeAt(i);
if (c1>=0xD800 && c1<0xDC00 && i+1<this.length) {
var c2= this.charCodeAt(i+1);
if (c2>=0xDC00 && c2<0xE000) {
chars.push(0x10000 + ((c1-0xD800)<<10) + (c2-0xDC00));
i++;
continue;
}
}
chars.push(c1);
}
return chars;
}
For the inverse to this see https://stackoverflow.com/a/3759300/18936
Another method using codePointAt:
String.prototype.toCodePoints = function () {
var arCP = [];
for (var i = 0; i < this.length; i += 1) {
var cP = this.codePointAt(i);
arCP.push(cP);
if (cP >= 0x10000) {
i += 1;
}
}
return arCP;
}
I have a string, 12345.00, and I would like it to return 12345.0.
I have looked at trim, but it looks like it is only trimming whitespace and slice which I don't see how this would work. Any suggestions?
You can use the substring function:
let str = "12345.00";
str = str.substring(0, str.length - 1);
console.log(str);
This is the accepted answer, but as per the conversations below, the slice syntax is much clearer:
let str = "12345.00";
str = str.slice(0, -1);
console.log(str);
You can use slice! You just have to make sure you know how to use it. Positive #s are relative to the beginning, negative numbers are relative to the end.
js>"12345.00".slice(0,-1)
12345.0
You can use the substring method of JavaScript string objects:
s = s.substring(0, s.length - 4)
It unconditionally removes the last four characters from string s.
However, if you want to conditionally remove the last four characters, only if they are exactly _bar:
var re = /_bar$/;
s.replace(re, "");
The easiest method is to use the slice method of the string, which allows negative positions (corresponding to offsets from the end of the string):
const s = "your string";
const withoutLastFourChars = s.slice(0, -4);
If you needed something more general to remove everything after (and including) the last underscore, you could do the following (so long as s is guaranteed to contain at least one underscore):
const s = "your_string";
const withoutLastChunk = s.slice(0, s.lastIndexOf("_"));
console.log(withoutLastChunk);
For a number like your example, I would recommend doing this over substring:
console.log(parseFloat('12345.00').toFixed(1));
Do note that this will actually round the number, though, which I would imagine is desired but maybe not:
console.log(parseFloat('12345.46').toFixed(1));
Be aware that String.prototype.{ split, slice, substr, substring } operate on UTF-16 encoded strings
None of the previous answers are Unicode-aware.
Strings are encoded as UTF-16 in most modern JavaScript engines, but higher Unicode code points require surrogate pairs, so older, pre-existing string methods operate on UTF-16 code units, not Unicode code points.
See: Do NOT use .split('').
const string = "ẞ🦊";
console.log(string.slice(0, -1)); // "ẞ\ud83e"
console.log(string.substr(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.substring(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.replace(/.$/, "")); // "ẞ\ud83e"
console.log(string.match(/(.*).$/)[1]); // "ẞ\ud83e"
const utf16Chars = string.split("");
utf16Chars.pop();
console.log(utf16Chars.join("")); // "ẞ\ud83e"
In addition, RegExp methods, as suggested in older answers, don’t match line breaks at the end:
const string = "Hello, world!\n";
console.log(string.replace(/.$/, "").endsWith("\n")); // true
console.log(string.match(/(.*).$/) === null); // true
Use the string iterator to iterate characters
Unicode-aware code utilizes the string’s iterator; see Array.from and ... spread.
string[Symbol.iterator] can be used (e.g. instead of string) as well.
Also see How to split Unicode string to characters in JavaScript.
Examples:
const string = "ẞ🦊";
console.log(Array.from(string).slice(0, -1).join("")); // "ẞ"
console.log([
...string
].slice(0, -1).join("")); // "ẞ"
Use the s and u flags on a RegExp
The dotAll or s flag makes . match line break characters, the unicode or u flag enables certain Unicode-related features.
Note that, when using the u flag, you eliminate unnecessary identity escapes, as these are invalid in a u regex, e.g. \[ is fine, as it would start a character class without the backslash, but \: isn’t, as it’s a : with or without the backslash, so you need to remove the backslash.
Examples:
const unicodeString = "ẞ🦊",
lineBreakString = "Hello, world!\n";
console.log(lineBreakString.replace(/.$/s, "").endsWith("\n")); // false
console.log(lineBreakString.match(/(.*).$/s) === null); // false
console.log(unicodeString.replace(/.$/su, "")); // ẞ
console.log(unicodeString.match(/(.*).$/su)[1]); // ẞ
// Now `split` can be made Unicode-aware:
const unicodeCharacterArray = unicodeString.split(/(?:)/su),
lineBreakCharacterArray = lineBreakString.split(/(?:)/su);
unicodeCharacterArray.pop();
lineBreakCharacterArray.pop();
console.log(unicodeCharacterArray.join("")); // "ẞ"
console.log(lineBreakCharacterArray.join("").endsWith("\n")); // false
Note that some graphemes consist of more than one code point, e.g. 🏳️🌈 which consists of the sequence 🏳 (U+1F3F3), VS16 (U+FE0F), ZWJ (U+200D), 🌈 (U+1F308).
Here, even Array.from will split this into four “characters”.
Matching those is made easier with the RegExp set notation and properties of strings proposal.
Using JavaScript's slice function:
let string = 'foo_bar';
string = string.slice(0, -4); // Slice off last four characters here
console.log(string);
This could be used to remove '_bar' at end of a string, of any length.
A regular expression is what you are looking for:
let str = "foo_bar";
console.log(str.replace(/_bar$/, ""));
Try this:
const myString = "Hello World!";
console.log(myString.slice(0, -1));
Performance
Today 2020.05.13 I perform tests of chosen solutions on Chrome v81.0, Safari v13.1 and Firefox v76.0 on MacOs High Sierra v10.13.6.
Conclusions
the slice(0,-1)(D) is fast or fastest solution for short and long strings and it is recommended as fast cross-browser solution
solutions based on substring (C) and substr(E) are fast
solutions based on regular expressions (A,B) are slow/medium fast
solutions B, F and G are slow for long strings
solution F is slowest for short strings, G is slowest for long strings
Details
I perform two tests for solutions A, B, C, D, E(ext), F, G(my)
for 8-char short string (from OP question) - you can run it HERE
for 1M long string - you can run it HERE
Solutions are presented in below snippet
function A(str) {
return str.replace(/.$/, '');
}
function B(str) {
return str.match(/(.*).$/)[1];
}
function C(str) {
return str.substring(0, str.length - 1);
}
function D(str) {
return str.slice(0, -1);
}
function E(str) {
return str.substr(0, str.length - 1);
}
function F(str) {
let s= str.split("");
s.pop();
return s.join("");
}
function G(str) {
let s='';
for(let i=0; i<str.length-1; i++) s+=str[i];
return s;
}
// ---------
// TEST
// ---------
let log = (f)=>console.log(`${f.name}: ${f("12345.00")}`);
[A,B,C,D,E,F,G].map(f=>log(f));
This snippet only presents soutions
Here are example results for Chrome for short string
Use regex:
let aStr = "12345.00";
aStr = aStr.replace(/.$/, '');
console.log(aStr);
How about:
let myString = "12345.00";
console.log(myString.substring(0, myString.length - 1));
1. (.*), captures any character multiple times:
console.log("a string".match(/(.*).$/)[1]);
2. ., matches last character, in this case:
console.log("a string".match(/(.*).$/));
3. $, matches the end of the string:
console.log("a string".match(/(.*).{2}$/)[1]);
https://stackoverflow.com/questions/34817546/javascript-how-to-delete-last-two-characters-in-a-string
Just use trim if you don't want spaces
"11.01 °C".slice(0,-2).trim()
Here is an alternative that i don't think i've seen in the other answers, just for fun.
var strArr = "hello i'm a string".split("");
strArr.pop();
document.write(strArr.join(""));
Not as legible or simple as slice or substring but does allow you to play with the string using some nice array methods, so worth knowing.
debris = string.split("_") //explode string into array of strings indexed by "_"
debris.pop(); //pop last element off the array (which you didn't want)
result = debris.join("_"); //fuse the remainng items together like the sun
If you want to do generic rounding of floats, instead of just trimming the last character:
var float1 = 12345.00,
float2 = 12345.4567,
float3 = 12345.982;
var MoreMath = {
/**
* Rounds a value to the specified number of decimals
* #param float value The value to be rounded
* #param int nrDecimals The number of decimals to round value to
* #return float value rounded to nrDecimals decimals
*/
round: function (value, nrDecimals) {
var x = nrDecimals > 0 ? 10 * parseInt(nrDecimals, 10) : 1;
return Math.round(value * x) / x;
}
}
MoreMath.round(float1, 1) => 12345.0
MoreMath.round(float2, 1) => 12345.5
MoreMath.round(float3, 1) => 12346.0
EDIT: Seems like there exists a built in function for this, as Paolo points out. That solution is obviously much cleaner than mine. Use parseFloat followed by toFixed
if(str.substring(str.length - 4) == "_bar")
{
str = str.substring(0, str.length - 4);
}
Via slice(indexStart, indexEnd) method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.
console.clear();
let str = "12345.00";
let a = str.slice(0, str.length -1)
console.log(a, "<= a");
console.log(str, "<= str is NOT changed");
Via Regular Expression method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.
console.clear();
let regExp = /.$/g
let b = str.replace(regExp,"")
console.log(b, "<= b");
console.log(str, "<= str is NOT changed");
Via array.splice() method -> this only works on arrays, and it CHANGES, the existing array (so careful with this one), you'll need to convert a string to an array first, then back.
console.clear();
let str = "12345.00";
let strToArray = str.split("")
console.log(strToArray, "<= strToArray");
let spliceMethod = strToArray.splice(str.length-1, 1)
str = strToArray.join("")
console.log(str, "<= str is changed now");
In cases where you want to remove something that is close to the end of a string (in case of variable sized strings) you can combine slice() and substr().
I had a string with markup, dynamically built, with a list of anchor tags separated by comma. The string was something like:
var str = "<a>text 1,</a><a>text 2,</a><a>text 2.3,</a><a>text abc,</a>";
To remove the last comma I did the following:
str = str.slice(0, -5) + str.substr(-4);
You can, in fact, remove the last arr.length - 2 items of an array using arr.length = 2, which if the array length was 5, would remove the last 3 items.
Sadly, this does not work for strings, but we can use split() to split the string, and then join() to join the string after we've made any modifications.
var str = 'string'
String.prototype.removeLast = function(n) {
var string = this.split('')
string.length = string.length - n
return string.join('')
}
console.log(str.removeLast(3))
Try to use toFixed
const str = "12345.00";
return (+str).toFixed(1);
Try this:
<script>
var x="foo_foo_foo_bar";
for (var i=0; i<=x.length; i++) {
if (x[i]=="_" && x[i+1]=="b") {
break;
}
else {
document.write(x[i]);
}
}
</script>
You can also try the live working example on http://jsfiddle.net/informativejavascript/F7WTn/87/.
#Jason S:
You can use slice! You just have to
make sure you know how to use it.
Positive #s are relative to the
beginning, negative numbers are
relative to the end.
js>"12345.00".slice(0,-1)
12345.0
Sorry for my graphomany but post was tagged 'jquery' earlier. So, you can't use slice() inside jQuery because slice() is jQuery method for operations with DOM elements, not substrings ...
In other words answer #Jon Erickson suggest really perfect solution.
However, your method will works out of jQuery function, inside simple Javascript.
Need to say due to last discussion in comments, that jQuery is very much more often renewable extension of JS than his own parent most known ECMAScript.
Here also exist two methods:
as our:
string.substring(from,to) as plus if 'to' index nulled returns the rest of string. so:
string.substring(from) positive or negative ...
and some other - substr() - which provide range of substring and 'length' can be positive only:
string.substr(start,length)
Also some maintainers suggest that last method string.substr(start,length) do not works or work with error for MSIE.
Use substring to get everything to the left of _bar. But first you have to get the instr of _bar in the string:
str.substring(3, 7);
3 is that start and 7 is the length.