Unexpected Result With JavaScript Substr()

I'm having a problem with substr() in JavaScript.

Please look at the code below.

The following works as expected. y = 2017

var add_date = "20170505";
var y = add_date.substr(0, 4);

alert(y);

But... the following doesn't work. It should return '05' but instead it returns 0505. m = 0505

var add_date = "20170505";
var m = add_date.substr(4, 6);
alert(m);

Could someone explain me what's wrong?

Thanks,

Nathan

Answer

.substr(4,6) method returns 6 characters starting at index 4. Use .substring instead.

var add_date = "20170505",
    y = add_date.substring(0, 4);
    console.log(y);


var add_date = "20170505",
    m = add_date.substring(4, 6);
    console.log(m);