How to Create a Function from a String with JavaScript

Is there a way to create a function from a string with javascript?

I added a jsperf test for 4 different ways to create a function from string :

• Using RegExp with Function class

  var func = "function (a, b) { return a + b; }".parseFunction();

• Using Function class with "return"

  var func = new Function("return " + "function (a, b) { return a + b; }")();

• Using official Function constructor

  var func = new Function("a", "b", "return a + b;");

• Using Eval

  eval("var func = function (a, b) { return a + b; };");

http://jsben.ch/D2xTG

2 result samples:

Given a string describing a Javascript function, convert it to a Javascript function

There's also the Function object.

var adder = new Function("a", "b", "return a + b");

How to turn a String into a JavaScript function call?

Seeing as I hate eval, and I am not alone:

var fn = window[settings.functionName];
if(typeof fn === 'function') {
    fn(t.parentNode.id);
}

Edit: In reply to @Mahan's comment:
In this particular case, settings.functionName would be "clickedOnItem". This would, at runtime translate var fn = window[settings.functionName]; into var fn = window["clickedOnItem"], which would obtain a reference to function clickedOnItem (nodeId) {}. Once we have a reference to a function inside a variable, we can call this function by "calling the variable", i.e. fn(t.parentNode.id), which equals clickedOnItem(t.parentNode.id), which was what the OP wanted.

More full example:

/* Somewhere: */
window.settings = {
  /* [..] Other settings */
  functionName: 'clickedOnItem'
  /* , [..] More settings */
};

/* Later */
function clickedOnItem (nodeId) {
  /* Some cool event handling code here */
}

/* Even later */
var fn = window[settings.functionName]; 
/* note that settings.functionName could also be written
   as window.settings.functionName. In this case, we use the fact that window
   is the implied scope of global variables. */
if(typeof fn === 'function') {
    fn(t.parentNode.id);
}

Create multiple functions from one javascript source as string

When running in a browser, you can dynamically add a script element and execute it with createContextualFragment:

function executeCode(code) {    document.head.appendChild(        document.createRange().createContextualFragment('<script>' + code + '<\/script>')    );}
// Democonst code = `function func1(){    console.log('This comes from func1')}
function func2(){    console.log('This comes from func2')}
function func3(){    console.log('This comes from func3')}`;
executeCode(code);
func1();func2();func3();

How to write a JavaScript function that takes a string and print out each letter of that string?

charAt accepts the character's index in the string as a parameter, not the character itself.

function myFunc(str) {  for (var i = 0; i < str.length; i++) {    console.log(str.charAt(i));  }}myFunc('abc');

How to execute a JavaScript function when I have its name as a string

Don't use eval unless you absolutely, positively have no other choice.

As has been mentioned, using something like this would be the best way to do it:

window["functionName"](arguments);

That, however, will not work with a namespace'd function:

window["My.Namespace.functionName"](arguments); // fail

This is how you would do that:

window["My"]["Namespace"]["functionName"](arguments); // succeeds

In order to make that easier and provide some flexibility, here is a convenience function:

function executeFunctionByName(functionName, context /*, args */) {
  var args = Array.prototype.slice.call(arguments, 2);
  var namespaces = functionName.split(".");
  var func = namespaces.pop();
  for(var i = 0; i < namespaces.length; i++) {
    context = context[namespaces[i]];
  }
  return context[func].apply(context, args);
}

You would call it like so:

executeFunctionByName("My.Namespace.functionName", window, arguments);

Note, you can pass in whatever context you want, so this would do the same as above:

executeFunctionByName("Namespace.functionName", My, arguments);

how to create a function that receives a string abcbdbd?

An example using map

const str = "abcbdef";

const array = str.split("");

const output = array.map((_, idx, arr) => arr.slice(0, idx + 1).join("."));

console.log(output);

JavaScript How to Create a Function that returns a string with number of times a characters shows up in a string

let str = prompt('type a string ') || 'taco'

function getcount(str) {
  str = str.split('')
  let obj = {}
  for (i in str) {
    let char = str[i]
    let keys = Object.getOwnPropertyNames(obj)
    if (keys.includes(char)) {
      obj[char] += 1
    } else {
      obj[char] = 1
    }
  }
  let result = ''
  Object.getOwnPropertyNames(obj).forEach((prop) => {
    result += prop + obj[prop]
  })
  return result
}

console.log(getcount(str))

Is there a way to create an arrow function from a string with javascript?

You can use eval to execute a string as code.

eval("() => { console.log('no') }")();

Or if you need some string interpolation:

const foo = 'bar';
eval(`() => { console.log('${foo}') }`)();

Be careful of malicious injection.

Edit: OP, you should be able to extrapolate what you need to do from here.

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