Node JS for loop does not work

Question

In node js, after running the for loop, descrip does not contain anything, no field written into the descrip array, why?

data = data['data'];
var course = data['course'];
data = data['sections'];
var descrip = new Array();
console.log(data.length);
for (var i = data.size - 1; i >= 0; i--) {
    var data = data[i];
    var section = data['section'];
    var day = data['day'];
    var date = data['date'];
    var start = data['start_time'];
    var end = data['end_time'];
    var location = data['location'];
    var res = 'Section: '+section+'\nDate: '+date+' '+day+'\nLocation: '+location+'\nStart: '+start+'\tEnd: '+end;
    descrip.push(res);
};

Don't you mean data.length? You're referring to data.size there. Using forEach(...) largely avoids this. — tadman
– tadman, Commented Mar 27, 2014 at 0:39

Aaron Dufour · Accepted Answer · 2014-03-27 00:40:11Z

2

Assuming you expect data to be an array, data.size - 1 will be -1 since data.size is null. So it will exit the loop immediately. You probably want data.length.

answered Mar 27, 2014 at 0:40

Aaron Dufour

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1 Comment

tadman Over a year ago

In Ruby size and length are synonymous, so this is easy to miss.

net.uk.sweet · Accepted Answer · 2014-03-27 00:46:19Z

The length of an array in JavaScript is returned by the length property:

for (var i = data.length - 1; i >= 0; i--) {
     // no block scope in JS, using data as a variable name here overwrites array
    // var data = data[i];
    var _data = data[i];
    var section = _data['section'];
    var day = _data['day'];
    var date = _data['date'];
    var start = _data['start_time'];
    var end = _data['end_time'];
    var location = _data['location'];
    var res = 'Section: '+section+'\nDate: '+date+' '+day+'\nLocation: '+location+'\nStart: '+start+'\tEnd: '+end;
    descrip.push(res);
};

Also, as pointed out in the comments by @Red Alert, you're overwriting your data variable in the for loop (JavaScript has no concept of block scope). I've renamed it _data, but you could probably come up with a more meaningful name to distinguish between the array and the element of the current iteration.

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