Using slice() in JavaScript

Question

I have difficulty understanding the use of slice() wrt to the following code, which doesn't fetch me the result I expected.

var cDate = "11-05-2016";
var m = cDate.slice(0,2);
var d = cDate.slice(3,2);
var y = cDate.slice(6);
console.log("Month is " + m);
console.log("Day is " + d);
console.log("Year is " + y);

This gives the following output:

Month is 11
Day is 
Year is 2016

I tried to slice with different strings. But every time I do it, it always gives me an empty string when I slice it from the middle of the string. Why is this?

"endSlice Optional. The zero-based index at which to end extraction. If omitted, slice() extracts to the end of the string. If negative, it is treated as sourceLength + endSlice where sourceLength is the length of the string (for example, if endSlice is -3 it is treated as sourceLength - 3)." — Evan Trimboli
– Evan Trimboli, Commented Dec 5, 2016 at 22:36
2nd parameter is not the length of slice like it is in substr. — epascarello
– epascarello, Commented Dec 5, 2016 at 22:40
tangentially, I would recommend .split('-') for this sort of thing rather than slice or substr as the numbers are more readable and a little less magical. var parts = cDate.split('-'); var m = parts[0]; var d = parts[1]; var y = parts[2]; — Blake O'Hare
– Blake O'Hare, Commented Dec 5, 2016 at 22:43
use slice when you know the indices of the characters in the string, use substr when you know the length of the substring you want — Punit
– Punit, Commented Dec 5, 2016 at 22:44

Dekel · Accepted Answer · 2016-12-05 22:43:11Z

3

From MDN:

The slice() method extracts a section of a string and returns a new string.

The syntax of slice is:

str.slice(beginSlice[, endSlice])

Note that the endSlice is the actual position in the string (and not how many chars to get from the beginSlice).

In your example - you can't slice a string from position 3 to position 2 (because it goes backwards), so you get an empty string.

edited Dec 5, 2016 at 22:43

answered Dec 5, 2016 at 22:40

Dekel

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1 Comment

Ammu Over a year ago

//Note that the endSlice is the actual position in the string (and not how many chars to get from the beginning// Oh Ok. I get it now. Thanks!

Oriol · Accepted Answer · 2016-12-05 22:40:13Z

2

You seem to be confusing slice with substr. The arguments mean different things:

slice( startIndex, endIndex )
substr( startIndex, length )

var cDate = "11-05-2016";
var m = cDate.substr(0,2); // "11"
var d = cDate.substr(3,2); // "05"
var y = cDate.substr(6); // "2016"
console.log("Month is " + m);
console.log("Day is " + d);
console.log("Year is " + y);

answered Dec 5, 2016 at 22:40

Oriol

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