Question

I have an array of strings. I want to trim each string in the array.

I thought using [].map() with ''.trim() would work…

[' a', ' b   ', 'c'].map(String.prototype.trim);

…but my console said…

TypeError: String.prototype.trim called on null or undefined

jsFiddle.

I can’t see any null or undefined values in my array.

String.prototype.trim() and Array.prototype.map() are defined in Chrome 17, which I’m using to test.

Why doesn’t this work? I get the feeling I have overlooked something obvious.

I realise I could loop or drop a function in there. That’s not the point of this question, however.

Answer 1

trim is on the String prototype, meaning that it expects the this context to be that of a string where as the map method on Array provides the current array item as the first argument and the this context being the global object.