Question

47

Javascript replace null

rated 0 times [ 51] [ 4] / answers: 1 / hits: 23521 / 11 Years ago, tue, april 30, 2013, 12:00:00

var p = null

var q = null;

(p == q) //false. as Expected.



p.replace(null, replaced) // outputs replaced. Not expected.

p.replace(null, replaced) //outputs replaced. Expected.



q.replace(null, replaced) // error.  Expected.

q.replace(null, replaced) //error. Expected.

Why? Does replace not differentiate between null and null?

I ask because I ran into a bug in angularjs:

replace((pctEncodeSpaces ? null : /%20/g), '+');

If for example, someone had a username of null and it was used as url, it would be replaced with + on any $http calls. e.g. GET /user/null.

Not that this scenario would occur often, but I'm more curious why replace treats null and null as the same thing. Does replace do a .tostring on null before it does the replacement? Is this just a quirk of Javascript?

I verified this on both IE and Chrome's implementations of replace.

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brooksb

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1 Year ago

answered 11 Years ago braydon · Accepted Answer

Yes, this is expected according to the spec for replace (bolded relevant line, or page 146 of the ECMA-262 final draft). The first argument is checked to see if it is a regex and if not, it has toString() called on it (well, converted to a string somehow).

15.5.4.11 String.prototype.replace(searchValue, replaceValue)

Let string denote the result of converting the this value to a string.

Cut for brevity

IfsearchValue is not a regular expression, let searchString be ToString(searchValue) and search string for the first occurrence of
searchString. Let m be 0.

Cut for brevity