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1 Basic grammar
setTimeout()A function is a timer function in JavaScript that allows us to execute specified code after a certain time interval. Its basic syntax is as follows:
setTimeout(callback, delay, arg1, arg2, ...)
Among them, the callback parameter is a function that will be executed after the specified delay time. The delay parameter is a time value in milliseconds specifying the delay time. You can also optionally pass some parameters to the callback function.
2 calling method
setTimeout()The function is called as follows:
let timerId = setTimeout(callback, delay, arg1, arg2, ...);
2.1 Calling method without passing parameters
function sayHello() {
console.log('Hello');
}
setTimeout(sayHello, 1000);
In this example, we define a function called sayHello and use setTimeout()the function to delay its execution after 1 second. When 1 second has elapsed, the console will output "Hello".
2.2 Calling method of parameter passing
Sample code:
function sayHelloSth(name) {
console.log(`Hello ${
name}!`);
}
// 在 3 秒后打印 "Hello World!"
setTimeout(sayHelloSth, 3000, 'World');
In the sample code above, we defined a sayHelloSth()function, which takes one parameter name. Then, use setTimeout()the function to call sayHelloSth()the function and specify a delay of 3 seconds. We also pass the string "World" as the third parameter to setTimeout()the function so that it can be passed to sayHelloSth()the function. Therefore, after 3 seconds, you will see the output "Hello World!" on the console.
3 cancel delayed execution
When setTimeout()the function is called, it immediately returns a unique timer ID, which we can use to cancel delayed execution. For example:
let timerId = setTimeout(function() {
console.log('This message will never be displayed');
}, 5000);
clearTimeout(timerId);
In this example, we use the setTimeout function to create a timer and assign it to timerIda variable. Then, we immediately use setTimeout()the function to cancel the timer. This means that after 5 seconds, no messages will be output to the console.