JS replacing all occurrences of string using variable

Question

I know that str.replace(/x/g, "y")replaces all x's in the string but I want to do this

function name(str,replaceWhat,replaceTo){
    str.replace(/replaceWhat/g,replaceTo);
}

How can i use a variable in the first argument?

Solution

The RegExp constructor takes a string and creates a regular expression out of it.

function name(str,replaceWhat,replaceTo){
    var re = new RegExp(replaceWhat, 'g');
    return str.replace(re,replaceTo);
}

If replaceWhat might contain characters that are special in regular expressions, you can do:

function name(str,replaceWhat,replaceTo){
    replaceWhat = replaceWhat.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
    var re = new RegExp(replaceWhat, 'g');
    return str.replace(re,replaceTo);
}

See Is there a RegExp.escape function in Javascript?

Comments

[pts]

This doesn't work as expected if replaceWhat contains regexp metacharacters, e.g. *, +, [.

[pts]

This is Firefox-specific, in Chrome it replaces only the first occurrence.

[Barmar]

@pts So does a literal regexp.

[dc5]

Then add this logic in as well: Is there a RegExp.escape function in Javascript?

[Hogan]

True... it had the "nonstandard" flag.

[dronus]

If used like the asker intended, this will give wrong results if metacharacters appear in replaceWhat. So better chose another answer!

[Barmar]

@dronus Isn't that what pts said in his comment? dc5 pointed to a workaround for that.

[dronus]

Yes, it is exactly what pts said. But that doesn't make the answer itself valid... maybe you like to edit it?

[tjcafferkey]

npmjs.com/package/stringinject

[thatOneGuy]

remember, you need to bind this to a new variable : stackoverflow.com/questions/12231644/…

[thatOneGuy]

remember, you need to bind this to a new variable : stackoverflow.com/questions/12231644/…

[Barmar]

@thatOneGuy Good catch, I've added a return to the functions. I was obviously focused on the regexp part, not the replace part.

[Freddy Daniel]

@Hogan this is not working currently please remove this answer or update with working solution.