JavaScript - Creating function object from function definition in a String

Question

In JavaScript, is there any way to create function object from function definition in a String?

Something similar to a JSON.parse for creating JSON from a String.

const parseFunction = (str)=> {
   // What should be implemented here?
   return func;
}
let funStr = parseFunction("function replacer(arg1) {console.log(arg1)}");

Why do you need this? Where is the function definition coming from? — Felix Kling
– Felix Kling, Commented Jun 9, 2021 at 11:34
You could use the Function constructor? new Function(str)? Just pass the function body instead — evolutionxbox
– evolutionxbox, Commented Jun 9, 2021 at 11:40
@felix-kling working on a JSON template based dashboard configuration.. couldn't find a better validator(lints) that accepts function as a value for a key.. also having function inside JSON makes it as an invalid JSON.. I want to hold function as value and also a valid JSON. So, just looking for options — Karthikeyan
– Karthikeyan, Commented Jun 9, 2021 at 11:56

Abhishek Sharma · Accepted Answer · 2021-06-09 11:44:50Z

1

Using eval invites a lot of security risks in your application. Javascript now has a alternative to that here

const parseFunction = (str)=> {
   return Function('"use strict";return (' + str + ')')();
}
let funStr = parseFunction("function(arg1) {console.log(arg1)}");

You try playing around it this is just for reference.

answered Jun 9, 2021 at 11:44

Abhishek Sharma

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1 Comment

Felix Kling Over a year ago

Just to make sure that people don't get the wrong impression: The only difference between direct eval and Function()() is the fact that the latter executes the code in global scope. There isn't anything else that makes it fundamentally more secure.

Karthikeyan · Accepted Answer · 2021-06-09 13:40:47Z

1

Just improvising Mr.@abhishek-sharma answer,

The function created using Function('"use strict";return (' + str + ')')(); will not be closure of current scope. In case if anyone want to access some variable in the current scope,

const parseFunction = (str) => {
  return Function(
    'varNameInStr',
    'return function() {return (' + str + ')}',
  )(varInCurrScope)();
};
parseFunction("function(){console.log(varNameInStr)}")

answered Jun 9, 2021 at 13:40

Karthikeyan

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