jquery stop loop function

When writing JavaScript programs using jQuery, loop functions are often used to traverse arrays or objects. But sometimes we need to stop the execution of the loop function, such as when a certain condition is met and the loop needs to be terminated. So how to stop the execution of the loop function? This article will introduce several methods.

1. Use the break statement

The JavaScript break statement can be used to break out of the loop. When using jQuery's each() function, you can use the break statement in the loop body to terminate the loop. For example:

$.each([1, 2, 3, 4, 5], function(index, value) {
  console.log(value);
  if (value === 3) {
    return false; // 等效于 break
  }
});

In this example, the $.each() method traverses an array and outputs the value of each element. When the value of the element is equal to 3, the role of the break statement comes into play. At this time, the loop is terminated, and the output result is:

1
2
3

Note that the return false and break statements here have the same effect, because inside the each() function, if the function returns false, it is equivalent to using the break statement Break out of the loop.

2. Use variable markers

In some cases, it may not be possible to directly use the break statement to terminate the loop. In this case, we can use a variable marker to achieve this. For example:

var stopped = false;
$.each([1,2,3,4,5], function(index, value){
  console.log(value);
  if(value == 3) {
    stopped = true;
    return false;
  }
});

if(stopped) {
  console.log('循环被停止了！');
}

Here we use a variable named stopped, and when iterates to 3, set it to true. Then the variable is judged after the loop. If it is true, it means the loop is stopped. However, it should be noted that if you have to use a marker variable every time, it may lead to poor readability of the code. At the same time, variable naming also needs to be careful.

3. Use the second parameter of $.each()

The $.each() function accepts two parameters (the first parameter is the traversed object, the second parameter is the callback function), and there is a third optional parameter, which indicates whether to abort the loop. When the third parameter is true, the loop will be aborted; False, the loop will continue.

For example:

$.each([1,2,3,4,5], function(index, value){
  console.log(value);
  if(value == 3) {
    return false;
  }
}, true);

The returned result is:

1
2
3

It is worth noting that if the third parameter is true, the value of the third parameter will act as a loop object. So we can also write like this:

$.each([1,2,3,4,5], function(index, value, stop){
  console.log(value);
  if(value == 3) {
    stop();
  }
}, true);

The advantage of this is: we can use the stop() function name instead of the return false statement to improve code readability. At the same time, we can also flexibly write our termination loop code in the stop() function.

4. Use other looping methods

There are other jQuery looping functions, such as map(), grep(), inArray(), etc., all of which have the function of aborting the loop. For example:

var arr = [1,2,3,4,5];
$.map(arr, function(val, i){
  console.log(val);
  if(val == 3) {
    return null;
  }
});

In this example, we are using the map() method. The map() method will execute the callback function once for each element in the array arr. When the element value of the array is equal to 3, we return a null value, which will omit the value 3 from the output list of the map() method. The output result is:

1
2
4
5

In addition, you can also use jQuery's grep() function to implement array filtering operations.

Summary:

The above are several ways to stop the loop function. Choose different methods according to the actual situation. Among them, the use of break statements and variable markers are more common and relatively simple and easy to understand. In addition, it is recommended not to blindly pursue the use of short and concise code. Readability and code maintainability are the most important.

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