问题
This question already has an answer here:
- What's the best way to break from nested loops in JavaScript? 15 answers
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?
回答1:
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;
}
}
}
}
回答2:
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);
}
回答3:
See Aaron's. Otherwise:
j=5;i=5 instead of break.
回答4:
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!
回答5:
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();
回答6:
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:
- http://www.devguru.com/Technologies/ecmascript/quickref/break.html
- http://www.daaq.net/old/javascript/index.php?page=js+exiting+loops&parent=js+statements
回答7:
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.
回答8:
Use function for multilevel loops - this is good way:
function find_dup () {
for (;;) {
for(;;) {
if (done) return;
}
}
}
回答9:
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;
}
}
})()
回答10:
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();
回答11:
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.
回答12:
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
回答13:
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);
}
}
}
回答14:
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;
};
回答15:
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