Replace a variable in a function with the value in javascript

Question

I am looking for a way to replace a variable in a function with its actual value. I am going to convert this function into a string and send via a HTTP request and thus need to convert the variables inside the function with their values.

let x = Math.random();

let funcString = function () {
    let y = x + 10;
    return y;
}.toString();

// Send funcString as a parameter

For eg. in the above code if I send funcString as it is, whoever receiving it will have no idea what is the value of x.

Since I am ultimately sending a string I would like to send

"function () {let y = 0.53 + 10; return y;}" (assuming Math.random() produced 0.53 at runtime).

Is there any way to do this?

I am doing this in a nodejs project so a npm module would be fine by me too.

It would probably be more efficient (and better practice) to just send an object containing all the current values of the variables. i.e., send {functionBody: "...", vars: {x: 0.53}}. That way you wouldn't have to do string replacements in the function and worry about injection, syntax errors, etc. — ATOMP
– ATOMP, Commented Nov 16, 2018 at 15:06
why are you doing this? the value of y is determined so why not send just the value? — Joey Gough
– Joey Gough, Commented Nov 16, 2018 at 15:06
I'd also echo the question of why do that at all instead of sending the result? What is the benefit of sending the function to be evaluated elsewhere when you have all the information in the current context? Usually if you do need to calculate something in a different context, you send the parameters but not the algorithm. — VLAZ
– VLAZ, Commented Nov 16, 2018 at 15:12
I am using Highcharts' export server to generate a chart and as such I need to send in custom functions. export.highcharts.com — Sayak Mukhopadhyay
– Sayak Mukhopadhyay, Commented Nov 16, 2018 at 15:13
@SayakMukhopadhyay but I don't see that sending any strings. There are parameters and a callback. Are you trying to pass the string as a callback instead of an actual function? — VLAZ
– VLAZ, Commented Nov 16, 2018 at 15:16

cнŝdk · Accepted Answer · 2018-11-16 15:31:39Z

1

Well if you are returning this function as a string, just use String#replace() method to replace x occurrence with its value.

This is how you should use it:

funcString.replace('x', x)

Demo:

let x = Math.random();

let funcString = function () {
    let y = x + 10;
    return y;
}.toString();

console.log(funcString.replace('x', x));

Edit:

If your variable has many occurrences and can be part of other variables just use a regex with replace method.

funcString.replace(/\bx\b/g, x)

Demo:

let x = Math.random();

let funcString = function () {
    let y = x + 10;
    let fix ='true';
    let z = x * 2;
    return y;
}.toString();

console.log(funcString.replace(/\bx\b/g, x));

edited Nov 16, 2018 at 15:31

answered Nov 16, 2018 at 15:09

cнŝdk

32.2k7 gold badges62 silver badges81 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Sayak Mukhopadhyay Over a year ago

I have considered using replace but the thing is my function can have many x within it. Although, I guess since it's my code after all, I can give it a unique name.

cнŝdk Over a year ago

Yes, it depends on your code, but in all cases you can use the variable name in a regex for replace.

Sayak Mukhopadhyay Over a year ago

Yeah, the global search works. I have just made sure to give a unique name to the variable I am replacing.

Artyom Amiryan · Accepted Answer · 2018-11-16 15:16:43Z

0

use replace with regex, g will search all x-es

let x = Math.random();

let funcString = function () {
    let y = x + 10;
    let a = x + 10;
    let b = x + 10;
    
    return y;
}.toString().replace(/x/g, x);

console.log(funcString);

answered Nov 16, 2018 at 15:16

Artyom Amiryan

2,9961 gold badge16 silver badges25 bronze badges

Collectives™ on Stack Overflow

Replace a variable in a function with the value in javascript

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related