Develop Reference

Convert Arrow function to function expression

I have a function with a map object:
function xml_encode(s)
{
return Array.from(s).map(c =>
{
var cp = c.codePointAt(0);
return ((cp > 127) ? '&#' + cp + ';' : c);
}).join('');
}
This has worked great except it has broken everything when running Internet Explorer 11.
I tried to rewrite the code using a function expression however I get a c is not defined:
function xml_encode(s)
{
return Array.from(s).map(function()
{
var cp = c.codePointAt(0);
return ((cp > 127) ? '&#' + cp + ';' : c);
}).join('');
}
Unfortunately this needs to be a public-facing function and I am required to support IE11 for now. How do I rewrite this function to work with IE11?

You're missing the argument of your function so try this
function xml_encode(s) {
return Array.from(s).map(function(c) {
var cp = c.codePointAt(0);
return ((cp > 127) ? '&#' + cp + ';' : c);
}).join('');
}

You are missing the c paramter to your anonymous function.
function xml_encode(s)
{
return Array.from(s).map(
function(c) {
//use charCodeAt for IE or use a polyfill
//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/codePointAt#Polyfill
var cp = c.codePointAt(0);
return ((cp > 127) ? '&#' + cp + ';' : c);
}
).join('');
}
Bonus:
You might want to use s.split('') instead of Array.from(s) for better performance and browser support. String.prototype.split is supported in every browser while Array.from is not supported in IE for example. split is also 30% faster on Chrome and 80% faster on FF on my PC.

Try to modify your code as below (you are missing an argument in the function):
function xml_encode(s) {
return Array.from(s).map(function (c) {
var cp = c.codePointAt(0);
return cp > 127 ? '&#' + cp + ';' : c;
}).join('');
}
Since, you are using Array.from and codePointAt function, they don't support IE Browser. To use them in the IE browser, we need to add the related popyfill before using this function.
Polyfill code as below (I have created a sample to test it, it works well on my side.):
// Production steps of ECMA-262, Edition 6, 22.1.2.1
if (!Array.from) {
Array.from = (function () {
var toStr = Object.prototype.toString;
var isCallable = function (fn) {
return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
};
var toInteger = function (value) {
var number = Number(value);
if (isNaN(number)) { return 0; }
if (number === 0 || !isFinite(number)) { return number; }
return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
};
var maxSafeInteger = Math.pow(2, 53) - 1;
var toLength = function (value) {
var len = toInteger(value);
return Math.min(Math.max(len, 0), maxSafeInteger);
};
// The length property of the from method is 1.
return function from(arrayLike/*, mapFn, thisArg */) {
// 1. Let C be the this value.
var C = this;
// 2. Let items be ToObject(arrayLike).
var items = Object(arrayLike);
// 3. ReturnIfAbrupt(items).
if (arrayLike == null) {
throw new TypeError('Array.from requires an array-like object - not null or undefined');
}
// 4. If mapfn is undefined, then let mapping be false.
var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
var T;
if (typeof mapFn !== 'undefined') {
// 5. else
// 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
if (!isCallable(mapFn)) {
throw new TypeError('Array.from: when provided, the second argument must be a function');
}
// 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
if (arguments.length > 2) {
T = arguments[2];
}
}
// 10. Let lenValue be Get(items, "length").
// 11. Let len be ToLength(lenValue).
var len = toLength(items.length);
// 13. If IsConstructor(C) is true, then
// 13. a. Let A be the result of calling the [[Construct]] internal method
// of C with an argument list containing the single item len.
// 14. a. Else, Let A be ArrayCreate(len).
var A = isCallable(C) ? Object(new C(len)) : new Array(len);
// 16. Let k be 0.
var k = 0;
// 17. Repeat, while k < len… (also steps a - h)
var kValue;
while (k < len) {
kValue = items[k];
if (mapFn) {
A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
} else {
A[k] = kValue;
}
k += 1;
}
// 18. Let putStatus be Put(A, "length", len, true).
A.length = len;
// 20. Return A.
return A;
};
}());
}
/*! https://mths.be/codepointat v0.2.0 by #mathias */
if (!String.prototype.codePointAt) {
(function () {
'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
var defineProperty = (function () {
// IE 8 only supports `Object.defineProperty` on DOM elements
try {
var object = {};
var $defineProperty = Object.defineProperty;
var result = $defineProperty(object, object, object) && $defineProperty;
} catch (error) { }
return result;
}());
var codePointAt = function (position) {
if (this == null) {
throw TypeError();
}
var string = String(this);
var size = string.length;
// `ToInteger`
var index = position ? Number(position) : 0;
if (index != index) { // better `isNaN`
index = 0;
}
// Account for out-of-bounds indices:
if (index < 0 || index >= size) {
return undefined;
}
// Get the first code unit
var first = string.charCodeAt(index);
var second;
if ( // check if it’s the start of a surrogate pair
first >= 0xD800 && first <= 0xDBFF && // high surrogate
size > index + 1 // there is a next code unit
) {
second = string.charCodeAt(index + 1);
if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
}
}
return first;
};
if (defineProperty) {
defineProperty(String.prototype, 'codePointAt', {
'value': codePointAt,
'configurable': true,
'writable': true
});
} else {
String.prototype.codePointAt = codePointAt;
}
}());
}
More detail information, please check the Array.from() method and the codePointAt() method

How to convert a string with arrays to an array [duplicate]

This question already has answers here:
Safely turning a JSON string into an object
(28 answers)
Closed 4 years ago.
How do I convert this piece of response into a valid array?
I want to perform an Object.map on the data:
var user_roles = "['store_owner', 'super_admin']";
This is not a valid JSON so I can't use JSON.parse

Right, most answers posted here suggest using JSON.parse and then get downvoted 3 times before getting deleted. What people overlook here is the lack of JSON-compliant quotation. The string IS, however, valid JavaScript. You can do the following:
const obj = {
thing: "['store_owner', 'super_admin']",
otherThing: "['apple', 'cookies']"
}
for (const key in obj) {
const value = obj[key];
obj[key] = eval(value);
}
console.log(obj);
Output will be a valid javascript object:
{"thing":["store_owner","super_admin"],"otherThing":["apple","cookies"]}
Be careful with eval(), though! javascript eval() and security
You can try it here: https://es6console.com/jjqvrnhg/

I took the polyfill for JSON.parse I found here
And replaced the meaning of a string to consist of '' single quote notation:
/*
json_parse.js
2016-05-02
Public Domain.
NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
This file creates a json_parse function.
json_parse(text, reviver)
This method parses a JSON text to produce an object or array.
It can throw a SyntaxError exception.
The optional reviver parameter is a function that can filter and
transform the results. It receives each of the keys and values,
and its return value is used instead of the original value.
If it returns what it received, then the structure is not modified.
If it returns undefined then the member is deleted.
Example:
// Parse the text. Values that look like ISO date strings will
// be converted to Date objects.
myData = json_parse(text, function (key, value) {
var a;
if (typeof value === "string") {
a =
/^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2}(?:\.\d*)?)Z$/.exec(value);
if (a) {
return new Date(Date.UTC(+a[1], +a[2] - 1, +a[3], +a[4],
+a[5], +a[6]));
}
}
return value;
});
This is a reference implementation. You are free to copy, modify, or
redistribute.
This code should be minified before deployment.
See http://javascript.crockford.com/jsmin.html
USE YOUR OWN COPY. IT IS EXTREMELY UNWISE TO LOAD CODE FROM SERVERS YOU DO
NOT CONTROL.
*/
/*jslint for */
/*property
at, b, call, charAt, f, fromCharCode, hasOwnProperty, message, n, name,
prototype, push, r, t, text
*/
var json_parse = (function () {
"use strict";
// This is a function that can parse a JSON text, producing a JavaScript
// data structure. It is a simple, recursive descent parser. It does not use
// eval or regular expressions, so it can be used as a model for implementing
// a JSON parser in other languages.
// We are defining the function inside of another function to avoid creating
// global variables.
var at; // The index of the current character
var ch; // The current character
var escapee = {
"\"": "\"",
"\\": "\\",
"/": "/",
b: "\b",
f: "\f",
n: "\n",
r: "\r",
t: "\t"
};
var text;
var error = function (m) {
// Call error when something is wrong.
throw {
name: "SyntaxError",
message: m,
at: at,
text: text
};
};
var next = function (c) {
// If a c parameter is provided, verify that it matches the current character.
if (c && c !== ch) {
error("Expected '" + c + "' instead of '" + ch + "'");
}
// Get the next character. When there are no more characters,
// return the empty string.
ch = text.charAt(at);
at += 1;
return ch;
};
var number = function () {
// Parse a number value.
var value;
var string = "";
if (ch === "-") {
string = "-";
next("-");
}
while (ch >= "0" && ch <= "9") {
string += ch;
next();
}
if (ch === ".") {
string += ".";
while (next() && ch >= "0" && ch <= "9") {
string += ch;
}
}
if (ch === "e" || ch === "E") {
string += ch;
next();
if (ch === "-" || ch === "+") {
string += ch;
next();
}
while (ch >= "0" && ch <= "9") {
string += ch;
next();
}
}
value = +string;
if (!isFinite(value)) {
error("Bad number");
} else {
return value;
}
};
var string = function () {
// Parse a string value.
var hex;
var i;
var value = "";
var uffff;
// When parsing for string values, we must look for " and \ characters.
if (ch === "\'") {
while (next()) {
if (ch === "\'") {
next();
return value;
}
if (ch === "\\") {
next();
if (ch === "u") {
uffff = 0;
for (i = 0; i < 4; i += 1) {
hex = parseInt(next(), 16);
if (!isFinite(hex)) {
break;
}
uffff = uffff * 16 + hex;
}
value += String.fromCharCode(uffff);
} else if (typeof escapee[ch] === "string") {
value += escapee[ch];
} else {
break;
}
} else {
value += ch;
}
}
}
error("Bad string");
};
var white = function () {
// Skip whitespace.
while (ch && ch <= " ") {
next();
}
};
var word = function () {
// true, false, or null.
switch (ch) {
case "t":
next("t");
next("r");
next("u");
next("e");
return true;
case "f":
next("f");
next("a");
next("l");
next("s");
next("e");
return false;
case "n":
next("n");
next("u");
next("l");
next("l");
return null;
}
error("Unexpected '" + ch + "'");
};
var value; // Place holder for the value function.
var array = function () {
// Parse an array value.
var arr = [];
if (ch === "[") {
next("[");
white();
if (ch === "]") {
next("]");
return arr; // empty array
}
while (ch) {
arr.push(value());
white();
if (ch === "]") {
next("]");
return arr;
}
next(",");
white();
}
}
error("Bad array");
};
var object = function () {
// Parse an object value.
var key;
var obj = {};
if (ch === "{") {
next("{");
white();
if (ch === "}") {
next("}");
return obj; // empty object
}
while (ch) {
key = string();
white();
next(":");
if (Object.hasOwnProperty.call(obj, key)) {
error("Duplicate key '" + key + "'");
}
obj[key] = value();
white();
if (ch === "}") {
next("}");
return obj;
}
next(",");
white();
}
}
error("Bad object");
};
value = function () {
// Parse a JSON value. It could be an object, an array, a string, a number,
// or a word.
white();
switch (ch) {
case "{":
return object();
case "[":
return array();
case "\'":
return string();
case "-":
return number();
default:
return (ch >= "0" && ch <= "9")
? number()
: word();
}
};
// Return the json_parse function. It will have access to all of the above
// functions and variables.
return function (source, reviver) {
var result;
text = source;
at = 0;
ch = " ";
result = value();
white();
if (ch) {
error("Syntax error");
}
// If there is a reviver function, we recursively walk the new structure,
// passing each name/value pair to the reviver function for possible
// transformation, starting with a temporary root object that holds the result
// in an empty key. If there is not a reviver function, we simply return the
// result.
return (typeof reviver === "function")
? (function walk(holder, key) {
var k;
var v;
var val = holder[key];
if (val && typeof val === "object") {
for (k in val) {
if (Object.prototype.hasOwnProperty.call(val, k)) {
v = walk(val, k);
if (v !== undefined) {
val[k] = v;
} else {
delete val[k];
}
}
}
}
return reviver.call(holder, key, val);
}({"": result}, ""))
: result;
};
}());
console.log(json_parse("['store_owner', 'super_admin']"));

Make it JSON compliant
JSON.parse(user_roles.replace(/(?<!\\)'/g,'"')
This works by fixing the reason why your code can't be parsed by JSON. That reason is that JSON doesn't let you use single quotes (') so we change them to Double Quotes (")
EDIT:
I made it so that when a ' is preceded by a \ it will not be replaced with a ".

Get function parameter length including default params

If you make use of the Function.length property, you get the total amount of arguments that function expects.
However, according to the documentation (as well as actually trying it out), it does not include Default parameters in the count.
This number excludes the rest parameter and only includes parameters before the first one with a default value
- Function.length
Is it possible for me to somehow get a count (from outside the function) which includes Default parameters as well?

Maybe you can parse it yourself, something like:
function getNumArguments(func) {
var s = func.toString();
var index1 = s.indexOf('(');
var index2 = s.indexOf(')');
return s.substr(index1 + 1, index2 - index1 - 1).split(',').length;
}
console.log(getNumArguments(function(param1, param3 = 'test', ...param2) {})); //3

Copying my answer over to here from a duplicate question:
Well, it's a bit of a mess but I believe this should cover most edge cases.
It works by converting the function to a string and counting the commas, but ignoring commas that are in strings, in function calls, or in objects/arrays. I can't think of any scenarios where this won't return the proper amount, but I'm sure there is one, so this is in no way foolproof, but should work in most cases.
UPDATE: It's been pointed out to me that this won't work for cases such as getNumArgs(a => {}) or getNumArgs(function(a){}.bind(null)), so be aware of that if you try to use this.
function getNumArgs(func) {
var funcStr = func.toString();
var commaCount = 0;
var bracketCount = 0;
var lastParen = 0;
var inStrSingle = false;
var inStrDouble = false;
for (var i = 0; i < funcStr.length; i++) {
if (['(', '[', '{'].includes(funcStr[i]) && !inStrSingle && !inStrDouble) {
bracketCount++;
lastParen = i;
} else if ([')', ']', '}'].includes(funcStr[i]) && !inStrSingle && !inStrDouble) {
bracketCount--;
if (bracketCount < 1) {
break;
}
} else if (funcStr[i] === "'" && !inStrDouble && funcStr[i - 1] !== '\\') {
inStrSingle = !inStrSingle;
} else if (funcStr[i] === '"' && !inStrSingle && funcStr[i - 1] !== '\\') {
inStrDouble = !inStrDouble;
} else if (funcStr[i] === ',' && bracketCount === 1 && !inStrSingle && !inStrDouble) {
commaCount++;
}
}
// Handle no arguments (last opening parenthesis to the last closing one is empty)
if (commaCount === 0 && funcStr.substring(lastParen + 1, i).trim().length === 0) {
return 0;
}
return commaCount + 1;
}
Here are a few tests I tried it on: https://jsfiddle.net/ekzuvL0c/

Here is a function to retrieve the 'length' of a function (expression or object) or an arrow function expression (afe). It uses a regular expression to extract the arguments part from the stringified function/afe (the part between () or before =>) and a regular expression to cleanup default values that are strings. After the cleanups, it counts the comma's, depending on the brackets within the arguments string.
Note This will always be an approximation. There are edge cases that won't be covered. See the tests in this Stackblitz snippet
const determineFnLength = fnLenFactory();
console.log(`fnTest.length: ${determineFnLength(fnTest)}`);
function fnTest(a,
b,
c = 'with escaped \' quote and, comma',
d = "and double \" quotes, too!" ) { console.log(`test123`); }
function fnLenFactory() {
const fnExtractArgsRE = /(^[a-z_](?=(=>|=>{)))|((^\([^)].+\)|\(\))(?=(=>|{)))/g;
const valueParamsCleanupRE = /(?<=[`"'])([^\`,].+?)(?=[`"'])/g;
const countArgumentsByBrackets = params => {
let [commaCount, bracketCount, bOpen, bClose] = [0, 0, [...`([{`], [...`)]}`]];
[...params].forEach( chr => {
bracketCount += bOpen.includes(chr) ? 1 : bClose.includes(chr) ? -1 : 0;
commaCount += chr === ',' && bracketCount === 1 ? 1 : 0; } );
return commaCount + 1; };
const extractArgumentsPartFromFunction = fn => {
let fnStr = fn.toString().replace(RegExp(`\\s|function|${fn.name}`, `g`), ``);
fnStr = (fnStr.match(fnExtractArgsRE) || [fn])[0]
.replace(valueParamsCleanupRE, ``);
return !fnStr.startsWith(`(`) ? `(${fnStr})` : fnStr; };
return (func, forTest = false) => {
const params = extractArgumentsPartFromFunction(func);
const nParams = params === `()` ? 0 : countArgumentsByBrackets(params);
return forTest ? [params, nParams] : nParams;
};
}

Javascript String Manipulation and Conversion with Range

I have a string like this (must be in this format):
var string = "[0] No new notifications | [1,] Some new notifications"
And I want to get "No new notifications" if a variable is 0 and if that variable is 1 or greater, show "Some new notifications".
How can I do that?

Here's a generic processesor for ISO 31-11 strings. It takes the ISO 31-11 string and the numeric value, then returns the appropriate string or undefined. Here's a fiddle.
function processISO31_11(rangeGuide, n) {
var separator = /\[(\d+)(,)?(\d+)?\]\s?(.+)/;
var rangeGuides = rangeGuide.split('|');
var guideCount = rangeGuides.length;
for (var guide = 0; guide < guideCount; guide++) {
var elements = separator.exec(rangeGuides[guide]);
if (elements != null) {
if (n < parseFloat(elements[1])) {
return; // return undefined indicating failure to match any range
}
if (n == parseFloat(elements[1])) {
return elements[4];
}
if (elements[2] === "," && (typeof elements[3] === "undefined" || n <= parseFloat(elements[3]))) {
return elements[4];
}
}
}
}

var somevar = 3;
var yourString = '[0] No new notifications | [1,] Some new notifications';
var notification = yourString .split(' | ');
var message=(somevar == 0 ? notification[0].split('] ')[1] : notification[1].split('] ')[1]);
the var message has your needed output.

After examining more closely exactly what you are looking for, I have come up with a solution that will read in the rules you pass it and essentially turn that into logic that your program will follow. Here is a demo of how it would work:
var myVar = 3;
var myStr = '[0] No new notifications | [1,4] Some new notifications | [5,] Several new notifications';
var notificationRules = getRules(myStr);
function getRules(rulesString) {
return rulesString.split(' | ').map(function(rule) {
var startValue, endValue;
var values = rule.match(/\[\d*,?\d*\]/g)[0];
values = values.replace(/\[|\]/g, "").split(",");
startValue = values[0];
endValue = +values[1] === 0 ? Infinity : values[1];
return {
startValue: Number(startValue),
endValue: endValue != undefined ? Number(endValue) : undefined,
message: rule.replace(/\[\d*,?\d*\]/g, "").trim()
};
});
}
function getMessage(myVar, rules) {
var message = "No rule match!";
rules.some(function(rule) {
if (myVar === rule.startValue) {
message = rule.message;
return true;
} else if (myVar >= rule.startValue && myVar <= rule.endValue) {
message = rule.message;
}
});
return message;
}
console.log(getMessage(0, notificationRules));
console.log(getMessage(2, notificationRules));
console.log(getMessage(5, notificationRules));
console.log(getMessage(100, notificationRules));
console.log(getMessage(-1, notificationRules));

Complex solution using String.prototype.split(), String.prototype.match() and String.prototype.slice() functions:
var configStr = '[0] No new notifications | [1,] Some new notifications',
getNotifyMessage = function (config, num) {
var num = Number(num),
items = config.split('|'),
len = items.length, parts;
while (len--) {
parts = items[len].match(/\[(\d+,?)\]\s([\w ]+)(?=\||$)/i);
if (Number(parts[1]) === num) {
return parts[2];
}
if (parts[1].slice(-1) === ',' && Number(parts[1].slice(0,-1)) <= num) {
return parts[2];
}
}
return '';
};
console.log(getNotifyMessage(configStr, 1));
console.log(getNotifyMessage(configStr, 0));
console.log(getNotifyMessage(configStr, 3));

a regex or function to extract all the parameters passed to a function

I am looking to find the passed parameter to a function
say i already have hello as function and i have a STRING as following
hello(1,'434','hello,word',"h,g",{a:'b,u', l : { "sk" : "list", bk : 'u,93' }, c : 9},true)
Then upon that regex or function i should be able to find following 6 strings
'1'
'"434"'
'"hello,world"'
'"h,g"'
'{"a":"b,u","l":{"sk":"list","bk": "u,93"},"c":9}'
'true'

As per urs question you can do it like this:
x =Hello(1,'434','hello,word',"h,g",{a:'b,u', l : { "sk" : "list", bk : 'u,93' }, c : 9},true);
function Hello() {
for (i = 0; i <arguments.length; i++) {
console.log(arguments[i])
}
}
You can take help of argument object which is an Array-like object corresponding to the arguments passed to a function.

If that's a string then you might have to escape the double quotes first to result like
var x = "hello(1,'434','hello,word',\"h,g\",{a:'b,u', l : { \"sk\" : \"list\", bk : 'u,93' }, c : 9},true)";
and then you may invoke it like
Function(x)();
and in the hello function you should iterate over the arguments object's properties like
function hello(){
Array.prototype.forEach.call(arguments, prop => console.log(prop));
}

This is my workaround. It may be error-prone, but it should be faster than the eval solutions.
var extractParameters = function(str){
var ar = [];
if(typeof str === 'string' && str.length){
var chars = str.split(','), cl = chars.length;
var pushInto = function(n){
try {
ar.push(JSON.parse(chars[n]));
} catch(er){
ar.push(undefined);
}
};
for(var di, si, eg, fg, n = 0; n < cl; n++){
eg = chars[n].charAt(0);
fg = chars[n].charAt(chars[n].length - 1);
if(eg === fg && (eg === '"' || eg === "'")){
chars[n] = "\"" + chars[n].substring(1, chars[n].length - 1) + "\"";
}
di = chars[n].indexOf('"');
si = chars[n].indexOf("'");
if(((si === -1) && (di === -1)) || (eg === fg && (eg === '"' || eg === "'")) ||
(chars[n].charAt(0) === "{" && chars[n].charAt(chars[n].length-1) === "}" && (chars[n].match(/\{/g).length === chars[n].match(/\}/g).length))){
pushInto(n);
} else if(n < (cl-1)) {
chars[n] = chars[n] + ','+ chars[n+1];
chars.splice(n+1,1);
n--;
cl--;
continue;
}
}
}
return ar;
};
fiddle : https://jsfiddle.net/jv0328tp/16/