for
-loopA traditional for
loop has three components:
These three components are separated from each other by a ;
symbol. Content for each of these three components is optional, which means that the following is the most minimal for
loop possible:
for (;;) {
// Do stuff
}
Of course, you will need to include an if(condition === true) { break; }
or an if(condition === true) { return; }
somewhere inside that for
-loop to get it to stop running.
Usually, though, the initialization is used to declare an index, the condition is used to compare that index with a minimum or maximum value, and the afterthought is used to increment the index:
for (var i = 0, length = 10; i < length; i++) {
console.log(i);
}
for
loop to loop through an arrayThe traditional way to loop through an array, is this:
for (var i = 0, length = myArray.length; i < length; i++) {
console.log(myArray[i]);
}
Or, if you prefer to loop backwards, you do this:
for (var i = myArray.length - 1; i > -1; i--) {
console.log(myArray[i]);
}
There are, however, many variations possible, like for example this one:
for (var key = 0, value = myArray[key], length = myArray.length; key < length; value = myArray[++key]) {
console.log(value);
}
… or this one …
var i = 0, length = myArray.length;
for (; i < length;) {
console.log(myArray[i]);
i++;
}
… or this one: