I tried this:
for(i = 0; i < 5; i++){
for(j = i + 1; j < 5; j++){
break(2);
}
alert(1);
}
only to get:
SyntaxError: missing;before statement
So, how would I break a nested loop in JavaScript?
You should be able to break to a label, like so:
function foo ()
{
dance:
for(var k = 0; k < 4; k++){
for(var m = 0; m < 4; m++){
if(m == 2){
break dance;
}
}
}
}
You need to name your outer loop and break that loop, rather than your inner loop - like this.
outer_loop:
for(i=0;i<5;i++) {
for(j=i+1;j<5;j++) {
break outer_loop;
}
alert(1);
}
See Aaron's. Otherwise:
j=5;i=5 instead of break.
loop1:
for (var i in set1) {
loop2:
for (var j in set2) {
loop3:
for (var k in set3) {
break loop2; // breaks out of loop3 and loop2
}
}
}
code copied from Best way to break from nested loops in Javascript?
Please search before posting a question. The link was the FIRST related question I saw on the left side of this page!
There are at least five different ways to break out of two or more loops:
1) Set parent(s) loop to the end
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
{
if (j === 2)
{
i = 5;
break;
}
}
}
2) Use label
fast:
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
{
if (j === 2)
break fast;
}
}
3) Use variable
var exit_loops = false;
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
{
if (j === 2)
{
exit_loops = true;
break;
}
}
if (exit_loops)
break;
}
4) Use self executing function
(function()
{
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
{
if (j === 2)
return;
}
}
})();
5) Use regular function
function nested_loops()
{
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
{
if (j === 2)
return;
}
}
}
nested_loops();
Unfortunately you'll have to set a flag or use labels (think old school goto statements)
var breakout = false;
for(i=0;i<5;i++)
{
for(j=i+1;j<5;j++)
{
breakout = true;
break;
}
if (breakout) break;
alert(1)
};
The label approach looks like:
end_loops:
for(i=0;i<5;i++)
{
for(j=i+1;j<5;j++)
{
break end_loops;
}
alert(1)
};
edit: label incorrectly placed.
also see:
In my opinion, it's important to keep your construct vocabulary to a minimum. If I can do away with breaks and continues easily, I do so.
function foo ()
{
var found = false;
for(var k = 0; (k < 4 && !found); k++){
for(var m = 0; (m < 4 && !found); m++){
if( m === 2){
found = true;
}
}
}
return found;
}
Be warned, after the loop, m and k are one larger that you might think. This is because m++ and k++ are executed before their loop conditions. However, it's still better than 'dirty' breaks.
EDIT: long comment @Dennis...
I wasn't being 100% serious about being 'dirty', but I still think that 'break' contravenes my own conception of clean code. The thought of having multi-level breaks actually makes me feel like taking a shower.
I find justifying what I mean about a feeling about code because I have coded all life. The best why I can think of it is is a combination of manners and grammar. Breaks just aren't polite. Multi level breaks are just plain rude.
When looking at a for statement, a reader knows exactly where to look. Everything you need to know about the rules of engagement are in the contract, in between the parenthesis. As a reader, breaks insult me, it feels like I've been cheated upon.
Clarity is much more respectful than cheating.
Wrap in a self executing function and return
(function(){
for(i=0;i<5;i++){
for (j=0;j<3;j++){
//console.log(i+' '+j);
if (j == 2) return;
}
}
})()
Use function for multilevel loops - this is good way:
function find_dup () {
for (;;) {
for(;;) {
if (done) return;
}
}
}
You return to "break" you nested for loop.
function foo ()
{
//dance:
for(var k = 0; k < 4; k++){
for(var m = 0; m < 4; m++){
if(m == 2){
//break dance;
return;
}
}
}
}
foo();
break doesn't take parameters. There are two workarounds:
Wrap them in a function and call
returnSet a flag in the inner loop and break again right after the loop if the flag is set.
You can break nested for loops with the word 'break', it works without any labels.
In your case you need to have a condition which is sufficient to break a loop.
Here's an example:
var arr = [[1,3], [5,6], [9,10]];
for (var a = 0; a<arr.length; a++ ){
for (var i=0; i<arr[a].length; i++) {
console.log('I am a nested loop and i = ' + i);
if (i==0) { break; }
}
console.log('first loop continues');
}
It logs the following:
> I am a nested loop and i = 0
> first loop continues
> I am a nested loop and i = 0
> first loop continues
> I am a nested loop and i = 0
> first loop continues
The return; statement does not work in this case. Working pen
The another trick is by setting the parent loop to reach the end and then break the current loop
function foo()
{
for(var k = 0; k < 4; k++){
for(var m = 0; m < 4; m++){
if(m == 2){
k = 5; // Set this then break
break;
}
console.log(m);
}
}
}
Break 1st loop:
for(i=0;i<5;i++)
{
for(j=i+1;j<5;j++)
{
//do something
break;
}
alert(1);
};
Break both loops:
for(i=0;i<5;i++)
{
var breakagain = false;
for(j=i+1;j<5;j++)
{
//do something
breakagain = true;
break;
}
alert(1);
if(breakagain)
break;
};
function myFunction(){
for(var i = 0;i < n;i++){
for(var m = 0;m < n;m++){
if(/*break condition*/){
goto out;
}
}
}
out:
//your out of the loop;
}
来源：https://stackoverflow.com/questions/1564818/how-to-break-nested-loops-in-javascript