Why does this javascript for loop cause an early exit? [duplicate]

Question

Right now I am really stumped. I have a short function, called "validate", and for some reason the for loop I have prevents an outer for loop from running.

Here it is breaking by only printing out the first entry:

function validate(str) {
    for(i=0; i<str.length; i++) {
        // do nothing
    }
    return str;
}

And here's the version that works:

function validate(str) {
    /*for(i=0; i<str.length; i++) {
        // do nothing
    }*/
    return str;
}

Here is my fiddle. Here is the sample text file.

post the code in the question, stackoverflow has same functionality as jsfiddle. but my guess is today you learn why var is not optional. — epascarello
– epascarello, Commented Aug 3, 2017 at 17:42

brenjt · Accepted Answer · 2017-08-03 17:43:24Z

3

Try encapsulating your variable i. var i = 0;

function validate(str) {
    for(var i = 0; i < str.length; i++) {
        // do nothing
    }
    return str;
}

Without the var you are adding it to the global scope or the window object

answered Aug 3, 2017 at 17:43

brenjt

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1 Comment

nosefouratyou Over a year ago

Thank you! I am indeed an idiot today. I'll accept your answer shortly (there is a waiting period apparently for accepting an answer).

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