Adding properties to javascript array at the moment of declaration?

Question

I know that we can add properties to an already defined array like this,

var array1 = [1, 2, 3];

array1.prop1 = 'first';
console.log(array1);  // [ 1, 2, 3, prop1: 'first' ]

My question is that is there any syntax for doing the same thing while declaring the array? Something similar to this,

var array1 = [1, 2, 3, prop1: 'first']  // SyntaxError: Unexpected token :

P.S. Some may say adding properties to arrays is not considered a good practice. That is actually not the answer I'm looking for. I'm just asking about the possibility of doing something like this.

Note that "extra" properties on array objects are fine, but if you serialize the array with JSON.stringify() they won't be included in the result. — Pointy
– Pointy, Commented Dec 4, 2019 at 13:55
Note that the output of console.log() will only contain the property on Chrome. All other browsers will only show the actual contents of the array. — NineBerry
– NineBerry, Commented Dec 4, 2019 at 14:03

Nina Scholz · Accepted Answer · 2019-12-04 13:56:39Z

3

You could take an object and assign this to an array.

var array1 = Object.assign([], { 0: 1, 1: 2, 2: 3, prop1: 'first' });

console.log(array1);
console.log(array1.prop1);

answered Dec 4, 2019 at 13:56

Nina Scholz

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5 Comments

Kobe Over a year ago

Would it be easier to read if you just spread [1,2,3]? As in { ...[1,2,3], prop1: 'first' }

deceze Over a year ago

ಠ_ಠ

Nina Scholz Over a year ago

@Kobe, yes, or no, because this code should never be used. it is for educational purpose only.

Nina Scholz Over a year ago

@deceze, please see above comment.

Kobe Over a year ago

@NinaScholz Sure, I only mentioned it to make it easier to write, not for actual use :P

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