Javascript Array Iteration - Mdn Example
I was reading the re-introduction to JavaScript on the MDN website and came across this example in the Array section: for (var i = 0, item; item = a[i++];){ // Do something with
Solution 1:
i++
is the post increment operator, which means that it increments i
by 1
but evaluates to the old (non-incremented) value.
> i = 0
0
> i++
0
> i
1
Solution 2:
i++ is post increment (see other answers) and item will not be undefined, because the predicate (the second part in the for loop) is executed before each iteration.
for (var i = 0, item ; item = a[i++];) {
will evaluate to:
var i = 0;
var item;
item = a[i]; // loop
i += 1if (!item) // exit loop// loop body// start again at loop
The problem with this syntax is, that if a value in a
is falsy, the loop will terminate prematurely.
var a = [1,2,0,3,4];
for (var i = 0, item ; item = a[i++];) {
console.log(item);
}
Will output "1 2" because "0" is falsy and the loop terminates
Solution 3:
i++ means that javascript reads the i value and then increments it
Post a Comment for "Javascript Array Iteration - Mdn Example"