javascript control method call

JavaScript is a widely used scripting language that can achieve many wonderful interactive effects. In JavaScript, we can use various methods (functions) to perform different tasks. But sometimes we need to control the calling of these methods under specific circumstances, which requires the use of some techniques to control method calling.

This article will introduce the techniques commonly used in JavaScript to control method calls, including conditional statements, loop statements, event binding and other methods. We will introduce these techniques one by one to help readers better understand how to control method calls in JavaScript.

1. Conditional Statement

Conditional statement is a commonly used technique to control method calls. It can execute different code blocks according to different conditions. In JavaScript, common conditional statements include if statements and switch statements.

1. if statement

The if statement is used to execute different blocks of code based on a condition. Its syntax structure is as follows:

if (条件表达式) {
    // 如果条件表达式为 true，则执行这里的代码块。
}

The following is a simple if statement example:

var age = 18;
if (age >= 18) {
    console.log("成年人");
} else {
    console.log("未成年人");
}

In the above example, if age is greater than or equal to 18, "adult" will be output, otherwise "Minor" will be output.

2. switch statement

The switch statement is used to execute different blocks of code based on multiple conditions. Its syntax structure is as follows:

switch (表达式) {
  case 值1:
    // 执行代码块 1
    break;
  case 值2:
    // 执行代码块 2
    break;
  default:
    // 执行默认代码块
}

The following is a simple switch statement example:

var day = 2;
switch (day) {
  case 1:
    console.log("星期一");
    break;
  case 2:
    console.log("星期二");
    break;
  case 3:
    console.log("星期三");
    break;
  default:
    console.log("其他");
}

In the above example, if day is equal to 1, "Monday" will be output, if day is equal to 2, "Tuesday" will be output. If day is equal to 3, "Wednesday" will be output, otherwise "Other" will be output.

2. Loop Statement

Loop statement is another commonly used technique to control method calls. It can repeatedly execute a piece of code until a specific condition is reached. In JavaScript, common loop statements include for loop, while loop and do-while loop.

1. for loop

The for loop is a commonly used loop statement that can execute a block of code based on specified conditions. The syntax structure is as follows:

for (初始化语句; 条件表达式; 增量表达式) {
  // 执行代码块
}

The following is a simple for loop example:

for (var i = 0; i < 10; i++) {
    console.log(i);
}

In the above example, the initial value of variable i is 0, and then the code block is executed in a loop, each time Increase by 1 until the value of i is greater than or equal to 10.

2. while loop

The while loop is also a commonly used loop statement, which can repeatedly execute a piece of code if specified conditions are met. The syntax structure is as follows:

while (条件表达式) {
  // 执行代码块
}

The following is a simple while loop example:

var i = 0;
while (i < 10) {
    console.log(i);
    i++;
}

In the above example, the initial value of variable i is 0, and then when the condition i<10 is met The code block is executed repeatedly, increasing by 1 each time, until the value of i is greater than or equal to 10.

3. do-while loop

The do-while loop is similar to the while loop, the only difference is that it will first execute the code block once and then check whether the condition is met. The syntax structure is as follows:

do {
  // 执行代码块
} while (条件表达式);

The following is a simple do-while loop example:

var i = 0;
do {
    console.log(i);
    i++;
} while (i < 10);

In the above example, the initial value of variable i is 0, and then the code block is executed once , execute the code block repeatedly under the condition that i<10, increasing by 1 each time until the value of i is greater than or equal to 10.

3. Event binding

Event binding is also a commonly used technique to control method calls, which can execute specified code when a specific event occurs. In JavaScript, common events include mouse events, keyboard events, form events, etc.

There are many ways to bind events. Common methods include direct binding, using event delegation, using third-party libraries, etc.

1. Direct binding

Direct binding is the most common event binding method, which can be implemented in HTML elements or through JavaScript. The syntax structure is as follows:

element.addEventListener(event, function, useCapture);

The following is a simple event binding example:

var btn = document.getElementById("btn");
btn.addEventListener("click", function() {
    alert("Hello world!");
});

In the above example, when the user clicks on the element with the id btn, a prompt box will pop up , displays "Hello world!".

2. Event delegation

Event delegation is an efficient way to bind events. It can bind an event to the container element instead of each child element. . When a child element fires an event, the event bubbles up to the container element, executing the corresponding code. The syntax structure is as follows:

container.addEventListener(eventType, function(event) {
  if (event.target.matches(selector)) {
    // 执行代码块
  }
});

The following is a simple event delegation example:

var list = document.getElementById("list");
list.addEventListener("click", function(event) {
    if (event.target.nodeName === "LI") {
        alert(event.target.innerHTML);
    }
});

In the above example, when the user clicks on the container element with the id of list, the click target will be determined Whether the element is a li element, if so, a prompt box will pop up to display the corresponding text content.

4. Summary

Control method calling techniques in JavaScript include conditional statements, loop statements, event binding and other methods. We can choose appropriate methods to control method calls according to different needs, thereby achieving more exciting interactive effects.

In actual development, we need to choose appropriate techniques according to specific situations and flexibly use various methods to achieve the required functions. At the same time, you also need to pay attention to controlling the number and frequency of method calls to avoid affecting web page performance and user experience.

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