Error when trim each string in an array

Question

If I trim each string in an array,

[' a ',' b','c '].map(i=>i.trim())

It works.

But [' a ',' b','c '].map(''.trim.call) will cause Uncaught TypeError: undefined is not a function.

I thought it should work...?

Yury Tarabanko · Accepted Answer · 2017-07-15 07:03:11Z

2

You need to bind call to String.prototyp.trim

[' a ','  b','c  '].map(''.trim.call.bind(''.trim))

[' a ','  b','c  '].map(Function.prototype.call.bind(''.trim))

Right now you simply get Function.prototype.call and then invoke it with undefined context

const call = Function.prototyp.call

[' a ','  b','c  '].map(call)

So each step is just call(item, index, array) while call uses this

answered Jul 15, 2017 at 6:58

Yury Tarabanko

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1 Comment

Thank you for your answer ! The explanation is very clear.