Each usage of javascript

JavaScript is a high-level, dynamic, object-oriented programming language that is widely used in web development, mobile applications, and desktop applications. Among them, the each loop is one of the most commonly used loop methods in JavaScript and has an extremely wide range of applications.

What is each?

each is a loop method specifically designed to iterate over data in an array or object. It is used as a iterator, which simplifies writing loops and makes the code easier to read and understand.

In JavaScript, each can use methods provided by different libraries or frameworks, for example, jQuery's $.each(), Underscore.js's _.each(), and Lodash's _.forEach() wait. This article will use Lodash’s each method as an example to explain.

How to use each?

For arrays:

Before using the each method provided by each library, we need to reference the library or framework before we can use the methods in it. In Lodash, we can use the following method to introduce the each method:

const _ = require('lodash');

Next, we can use the _.each() method to traverse the array, the code is as follows:

let arr = ['apple', 'banana', 'pear']; _.each(arr, function(fruit) { console.log(fruit); });

The above code , we traverse an array arr, and then use an anonymous function as a callback function to output the value of each element to the console.

In this example, we use an anonymous function to print each fruit. But we can also use a simpler way of writing to handle the above example. For example, we can use arrow functions to replace traditional anonymous functions:

_.each(arr, fruit => console.log(fruit));

This method is more concise and easier to read, and it is also very suitable for simplification of anonymous functions with only one line of code.

For objects:

When using each to traverse objects, we need to modify the parameters in the each method, for example:

let obj = {name: 'Tom', age: 18}; _.each(obj, function(value, key) { console.log(key + ': ' + value); });

In the above code, we use an object obj, and traverse it through the each method, and output the object's key-value pairs to the console. The key and value of each object will be passed to the callback function as parameters respectively.

valueOf

For Lodash's _.each() method, there is another method that is different from the default per-item processing logic, which is the valueOf() method. If we use the valueOf() method, the callback function specifies that the first parameter is always passed in the value returned by valueOf(). For example:

let obj = {name: 'Tom', age: 18}; _.each(obj, function(value, key) { console.log(value); }, function() { return this.age; }.valueOf());

In the above code, we use the valueOf() method and return the age of the object in the callback function. Therefore, on the console, only the object's age of 18 is output.

Summary:

Through the above examples, we can see that the each loop is very common and practical in JavaScript. It can traverse all types of data structures, and compared with the traditional for loop, it has the advantages of being more concise, easier to read, and easier to write. More importantly, it is widely used in most JavaScript libraries or frameworks, making the code more standardized and easier to maintain and extend.

Although different JavaScript libraries or frameworks implement each method and parameters slightly differently, in general, their purposes and functions are consistent. Therefore, in practical applications, we can flexibly choose according to project needs and team habits.

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