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so i was checking @robbmj 's answer to this question, and i came across the following code:

var timer = duration, minutes, seconds;

and another one here:

var start = Date.now(),
    diff,
    minutes,
    seconds;

I have never been to that code before. Could someone please explain what those two lines of code does or at least how to read them ?

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6
  • E.g. var timer = duration, minutes = x, seconds = y; ... minutes and seconds is declared but w/o any initial values Commented Apr 23, 2018 at 15:18
  • Those are just declarations. diff, minutes, and seconds will still be undefined. This can help make var declarations more obvious since you will have to worry about hoisting. Commented Apr 23, 2018 at 15:18
  • the first one set a var timer = duration and then 2 null / undefined vars - minutes and seconds. The second sets start as the current date and then sets three null / undefined vars in the scope. Basically if you follow your variable declaration with a comma, it means you can go directly into declaring another variable in that scope without the need for saying var again: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… Commented Apr 23, 2018 at 15:20
  • It's just this code: var timer = duration; var minutes; var seconds; condensed a little, timer is set to duration, minutes and seconds are undefined. Same thing applies to the second example, where start is defined as the value of Date.now() and the other variables are "initialized" Commented Apr 23, 2018 at 15:20
  • So it was that simple!! Thank you LGSon , zero298 , pete , luca :)) Commented Apr 23, 2018 at 15:24

4 Answers 4

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5

You can also use destructuring like this:

let [a, b, c] = [0, 0, 0]
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3

You can write 

var start = Date.now(),
diff,
minutes,
seconds;

as 

var start = Date.now();
var diff;
var minutes;
var seconds;

So you can declare multiple variables in one line as in code snippet 1 where we are initialising start but only declaring other variables.

You can initialise multiple in one line like

var a = 1, b = 2, c = 3;
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3 Comments

@jes Welcome :)
e.g. timer = 1; so --timer < 0 will be false. --timer will first decrement timer and then it will compare as compared to timer -- < 0 will first compare and then decrement.
yes I just read in here developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… big thanks to you again :))
0

your second example just separated with line breaks.

define multiple variables on a single line annoying to remove the first or last declaration because they contain the var keyword and semicolon. And every time you add a new declaration, you have to change the semicolon in the old line to a comma.

As a result, define multiple variables on a single line not recommended

using it

var timer = duration;
var minutes = 0;
var seconds = 0;

instead of 

var timer = duration, minutes, seconds;
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Comments

0

The First line creates 3 variables: timer, minutes and seconds. but is assigning the value of the variable duration to variable timer.

the same story in example 2, just separated with line breaks.

It is a shortened way of saying

var timer = duration;
var minutes;
var seconds;
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4 Comments

var a = 0 is not the same as var a;!
Yes, that's true, sorry.
Thank you @JacobSchneider :)
No worries. Pleased to help.