JavaScript array `push` with square brackets instead of parentheses - no error?

Question

I did this by accident...

var numbers = [1, 2, 3, 4];
numbers.push[5];

Why wasn't there an error message?

push needs parentheses, not square brackets. It was just a simple typo. I wasn't paying close enough attention to what I was doing... but why wasn't there an error message?

As far as I can tell, the numbers array wasn't modified in any way. It just did... nothing.

because that simply evaluates to undefined - any property (functions are just properties in javascript anyway) can have properties ... — Jaromanda X
– Jaromanda X, Commented Jan 14, 2018 at 23:20
Because it is just accessing the property named 5 on the property named push. There isn't a syntax error there, just a logic one — Patrick Evans
– Patrick Evans, Commented Jan 14, 2018 at 23:21

Devan Buggay · Accepted Answer · 2018-01-15 01:10:24Z

9

numbers.push is simply a function but you are attempting to find the property located at key 5 from it, which will evaluate to undefined.

function test() {
  console.log("test");
}


// test[5] evaluates to `undefined` and does nothing
console.log(test[5]);

// We can even manually set this without messing up the function
test[5] = "foo";

// outputs "foo"
console.log(test[5]);

// outputs our expected value "test"
test();

edited Jan 15, 2018 at 1:10

answered Jan 14, 2018 at 23:22

Devan Buggay

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