apply method not returning full array value in javascript

Question

I made an array to be passed in apply method, I was expecting to return full value of array, but when I used index value of array to give value of that index, array method actually returned index of character:

var obj = {
  name: 'Dogs'
}
var arr = ['India', 'Slovenia', 'Scotland'];

var getanimalsinfo = function(a) {

  return this.name + ' is good animal found in ' + a[2]

}
console.log(getanimalsinfo.apply(obj, arr));

Here, I was expecting "Dog is good animal found in Scotland", but I got : 'Dog is good animal found in d'. Here d is the third index of India. Please let me know what I did wrong. Thanks.

Felix Kling · Accepted Answer · 2018-12-06 08:19:10Z

6

.apply passes each element of the array as separate argument to the function. I.e. in your case the function is called as getanimalsinfo(arr[0], arr[1], arr[2]) and hence a will have the value 'india'.

If you want to pass the array as a single argument (equivalent to getanimalsinfo(arr)), use .call instead:

var obj = {
  name: 'Dogs'
}
var arr = ['india', 'slovenia', 'scotland'];

var getanimalsinfo = function(a) {

  return this.name + ' is good animal found in ' + a[2]

}
console.log(getanimalsinfo.call(obj, arr));
//                         ^^^^

Alternative solutions:

Wrap the argument passed to .apply in another array: getanimalsinfo.apply(obj, [arr])
Use a rest parameter in your function definition: function(...a) { /*...*/ }

Have a look at the MDN documentation for more info:

Javascript call() & apply() vs bind()?

edited Dec 6, 2018 at 8:19

answered Dec 6, 2018 at 8:08

Felix Kling

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5 Comments

user3450590 Over a year ago

ok, then how to get this result: 'dog is good animal found in india, slovenia, scotland' using APPLY??

Nika Over a year ago

@user3450590 with .call instead of .apply.

Felix Kling Over a year ago

@user3450590: If you defined the function as function(...args) {...} and did ' is good animal found in ' + args.join(). But you shouldn't define the function based on the fact that you want to use .apply. You should decide first whether you want the function to be variadic or accept an array as argument. And based on that you choose either .apply or .call.

Cid Over a year ago

@FelixKling with apply, he should have used function(arg1, arg2, arg3) instead of function(a) ?

Felix Kling Over a year ago

@Cid: Really depends on how the function should work.

Mamun · Accepted Answer · 2018-12-06 08:15:13Z

1

You can use arguments:

var obj={name: 'Dogs'};
var arr=['india','slovenia','scotland'];

var getanimalsinfo = function(){
    return this.name + ' is good animal found in '+ arguments[2]

}
console.log(getanimalsinfo.apply(obj, arr));

answered Dec 6, 2018 at 8:15

Mamun

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