A brief analysis of JavaScript deletion methods and precautions

JavaScript is a widely used programming language, often used in website development, game production and other fields. In the process of using JavaScript to develop, we sometimes need to delete some code or data. This article will introduce in detail the JavaScript deletion method and precautions.

1. Delete variables

In JavaScript, we can use the "delete" keyword to delete a variable. The example is as follows:

var a = 10;
delete a;
console.log(a); // 输出undefined

In the above code, we Use the delete keyword to delete variable a. At this time, operating on variable a will return undefined. It should be noted that using the delete keyword can only delete variables defined through var, let, const, etc., but not global variables or functions.

2. Delete attributes

We can also use the "delete" keyword to delete the attributes of an object. The example is as follows:

var obj = {
  name: "小明",
  age: 20
};
delete obj.name;
console.log(obj); // 输出{age: 20}

In the above code, we use delete The keyword deletes the name attribute of the obj object, and the output result is {age: 20}. It should be noted that using the delete keyword can only delete its own properties, not properties inherited from the parent object, for example:

var obj1 = Object.create({name: "小明"});
delete obj1.name;
console.log(obj1); // 输出{name: "小明"}

In the above code, we use the Object.create method to create an object obj1 , it inherits from an object {name: "Xiao Ming"}. Although the attribute name is deleted using the delete keyword, the final output result is still the original attribute {name: "Xiao Ming"}, because obj1 itself does not have this attribute.

3. Array deletion

In addition to using the "delete" keyword to delete an element in an array in JavaScript, you can also use the "splice" method to delete multiple elements. The example is as follows:

var arr = ["小明", "小王", "小红", "小李"];
arr.splice(1, 2);
console.log(arr); // 输出["小明", "小李"]

In the above code, we use the splice method to delete 2 elements starting from the first element in the array arr, and the final output result is ["Xiao Ming", "Xiao Li"]. It should be noted that the splice method can not only delete elements, but also insert and replace elements. For specific usage, please refer to the official JavaScript documentation.

4. Event deletion

In JavaScript, we sometimes need to delete an event listener. In this case, we can use the removeEventListener method to achieve this. The example is as follows:

var btn = document.getElementById("btn");
function clickHandler() {
  console.log("按钮被点击了");
}
btn.addEventListener("click", clickHandler);
btn.removeEventListener("click", clickHandler);

In In the above code, we first use the addEventListenr method to add a click event listener to the button, and then use the removeEventListener method to delete the event listener.

It should be noted that when adding an event listener, you need to retain a reference to the function, so that you can use the removeEventListener method to delete the listener later. If you use an anonymous function when adding an event listener, you cannot remove the listener later.

5. Summary

This article introduces several commonly used deletion methods in JavaScript such as deleting variables, deleting attributes, deleting arrays, and deleting events. They can help us be more flexible during the running of the code. Manage data, events, etc. At the same time, you need to pay attention to some details during use, such as the delete keyword that can only delete its own attributes.

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