Javascript replace a string with a function

Question

For example, i have:

var obj = { "Age": "{{Range(20, 50)}}" }
getRandomRange = function(min, max) {
 return Math.floor(Math.random() * (max - min)) + min;
}

I want to replace {{Range(20, 50)}} with function getRandomRange(20,50), something like this:

var new_obj = str.replace( /{{Range(x, y)}}/g, getRandomRange(x, y) );

Expected result: obj = { "Age": "30" }

How do i do this, could this be achieved with replace() only?

Thanks.

• Maheer Ali: Even if you replace it will be a string. The function will not be called or callable.

Answer 1

You could get the JSON string and replace the placeholder with a call of the function.

const
 json = '{ "Age": "{{Range(20, 50)}}" }',
 getRandomRange = (min, max) => Math.floor(Math.random() * (max - min)) + min,
 placeholder = /\{\{Range\((\d+),\s*(\d+)\)\}\}/g,
 targetjson = json.replace(placeholder, (_, x, y) => getRandomRange(+x, +y));
console.log(JSON.parse(targetjson));

• Bao Pham: Hi @NinaScholz. Your solution is worked. Thank you. Can you explain this part (_, x, y) => getRandomRange(+x, +y). I'm not quite understand this function call.
• Nina Scholz: the replacement function gets the paramter from the regular expression. this returns three parts: the first contains all matched values, the second the first group, the forthcoming first parameter x and the other group for the second parameter. by keeping your random function, it need another function to hand over the parameter and the wanted type as numbers.
• Bao Pham: I get it now. Thanks @Nina.

Answer 2

This is too much to put into a comment so I'm going to explain why its not working here:

1. str is not a string.

• Rename it because it can be msleading.

var obj = { "Age": "{{Range(20, 50)}}" }

2. replace method returns a string, not an object

• rename your variable to str.
• Also, special characters need to be backslahed: \{
• Also your method is being invoked, not actually being passed to the callback. Pass: getRandomRange not getRandomeRange(x, y)
• also - because you have 1 parenthesis in your regex below, it would return 2 arguments 0 and 1, but 1 is both (x, y), 0 = the whole match - {{Range(x, y)}}

var str = str.replace( /\{\{Range(x, y)\}\}/g, getRandomRange );

3. How to extract something close to your requirement?

• you don't need regex

getRandomRange = function(min, max) {
 return Math.floor(Math.random() * (max - min)) + min;
}
var obj = {"Age": getRandomRange(20, 50)}

4. if you want your result to be a string of a number

getRandomRange = function(min, max) {
 return Math.floor(Math.random() * (max - min)) + min;
}
var obj = {"Age": String(getRandomRange(20, 50))}

Lastly: Be clare or 'clear' about your types. string, object, number.

• Bao Pham: sr i've named it wrong. already edit my question. the reason for this is because i need to replace template inside double brackets {{ }} with a function.
• Inspiraller: @BaoPham You cannot do it with regex. The return of a replace method will be a string, not an object
• Bao Pham: i have my answer with NinaScholz helped. Thanks
• Inspiraller: @BaoPham That's good. Though I'd say its not a practice that should be encouraged. I say that as someone who loves regex, but this is not something I would ever do. I would encourage understanding simpler solutions.
• Bao Pham: can you provide me a solution to replace a template variable with a function call without using regex? I would appreciate it if it's simpler. Thanks.