How to trim a string to N chars in Javascript?

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How can I, using Javascript, make a
function that will trim string passed as argument, to a specified length, also passed as
argument. For
example:

var string =
            "this is a string";
var length = 6;
var trimmedString =
            trimFunction(length, string);

// trimmedString should
            be:
// "this
            is"

Anyone got ideas?
I've heard something about using substring, but didn't quite
understand.

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class="normal">Answer

Why not
just use substring... string.substring(0, 7); The first
argument (0) is the starting point. The second argument (7) is the ending point
(exclusive). href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/substring"
rel="noreferrer">More info
here.

var string = "this
            is a string";
var length = 7;
var trimmedString =
            string.substring(0, length);