Example of usage method of forEach in Vue

Preface

forEach() is a method of operating arrays in front-end development. The main function is to traverse arrays, which is actually an upgraded version of for loops. This statement requires a callback function as a parameter. The formal parameters of the callback function are: 1. value: iterates over the contents of the array; 2. index: the index of the corresponding array, and 3. array: the array itself.

In the Vue project, the loop in the tag uses v-for, and the loop in the method uses forEach.

Principle of use forEach()

The forEach() method is mainly used to call each element of the array and pass the elements to the callback function. It should be noted that the forEach() method will not execute callback functions for empty arrays.

forEach: that is, a method that only arrays have, which is equivalent to looping through an array.

Usage: (function(item,index,array){…}), where the callback function has 3 parameters, item is the element currently traversed, index is the subscript of the element currently traversed, and array is the array itself.

The forEach method does not skip null and undefined elements. For example, the four elements in the array [1, undefined, null, 2] will be traversed, pay attention to the difference from map.

forEach() syntax

example:

(function(item,index,array) { ... })

forEach() Other related content

① ForEach() continue and break: forEach() itself does not support the continue and break statements, but can be implemented through some and every.

②Difference between forEach() and map: forEach() has no return value, which is equivalent to a for loop in nature, and executes a function function for each item. That is, map returns a new array, the original array remains unchanged, and forEach changes the original array.

③Comparison between forEach() and for loop: The for loop steps are more complicated, and the forEach loop is relatively simple and easy to use, and is not prone to errors.

forEach() example

Example 1

let array = [1, 2, 3, 4, 5, 6, 7];
(function (item, index) {
    (item); //Open each element of the array});

Example 2

var array=[1, 2, 3, 4, 5];
(function(item, index, array) {
array[index]=4 * item;
} );
(array); // Output result：Modified the original array element，Multiply each element by4

Example 3

  <el-checkbox v-for="(item) in searchContent"
                       :label=""
                       :key=""
                       class="checkbox">
            <span>{{}}{{}}</span>
          </el-checkbox>
  handle(index, row) {
        =[];
        let a = this;
         = true;
         = ;
        this.$(“/user/resources", {
            params: {userId: }
          }).then((response) => {
           = ;
          (function (b) {
            if(b[‘checked']){
              ();
            }
          })
        })

Attach: ForEach in vue is not defined

In Vue, forEach is a method of JavaScript arrays that iterates through each element in the array and executes the specified callback function. If you get an "undefined" error when using the forEach method in Vue, it may be because you are trying to use the forEach method on an object that is not an array.

Make sure you apply it to a valid array object before using the forEach method. You can use the() method to check whether an object is an array. If it is not an array, you can try converting it to an array, or use other suitable methods to iterate over the properties of the object.

Here is a sample code that demonstrates how to use the forEach method correctly in Vue:

// Suppose you have an array called "items"data() {
  return {
    items: [1, 2, 3, 4, 5]
  }
},
mounted() {
  // Use the forEach method to traverse the array  (item => {
    (item);
  });
}

Make sure you have correctly defined the array object before using the forEach method and there are no typos or other syntax errors.

Summarize

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