What are the global functions in node?

Global functions: 1. setTimeout() function, used to execute the specified function after specified milliseconds; 2. clearTimeout() function, used to stop the timer created by setTimeout(); 3. setInterval(cb, ms) function, used to set the timer and return a handle value.

The operating environment of this article: Windows 10 system, nodejs version 12.19.0, Dell G3 computer.

What are the global functions in node

1. Timer function:

There are 4 in total, namely: setTimeout(), clearTimeout() , setInterval(), clearInterval().

setTimeout(cb, ms)

setTimeout(cb, ms) global function executes the specified function (cb) after the specified number of milliseconds (ms). :setTimeout() only executes the specified function once. Returns a handle value representing the timer.

Example

Create the file main.js, the code is as follows:

function printHello(){
   console.log( "Hello, World!");
}
// 两秒后执行以上函数
setTimeout(printHello, 2000);

Execute the main.js file, the code is as follows:

$ node main.js
Hello, World!
clearTimeout(t)

clearTimeout (t) The global function is used to stop a timer previously created through setTimeout(). Parameter t is the timer created through the setTimeout() function.

Example

Create the file main.js, the code is as follows:

function printHello(){
   console.log( "Hello, World!");
}
// 两秒后执行以上函数
var t = setTimeout(printHello, 2000);
// 清除定时器
clearTimeout(t);

Execute the main.js file, the code is as follows:

$ node main.js
setInterval(cb, ms)

setInterval The (cb, ms) global function executes the specified function (cb) after the specified number of milliseconds (ms). Returns a handle value representing the timer. You can use the clearInterval(t) function to clear the timer. The setInterval() method will continue to call the function until clearInterval() is called or the window is closed.

Example

Create the file main.js, the code is as follows:

function printHello(){
   console.log( "Hello, World!");
}
// 两秒后执行以上函数
setInterval(printHello, 2000);

Execute the main.js file, the code is as follows:

$ node main.js

Above The program will output "Hello, World!" every two seconds and will execute forever until you press the ctrl c button.

2. require function: used to load modules.

The parameter is the module file name with the full path, or directly the module name

require.main: used to detect whether a module is the main module in the application (written in Inside the detected module file)

if(module === require.main){
    console.log('true')
}

Multiple references to the same module will not cause multiple executions of the code in the module

require.resolve: Query a module file with complete absolute The file name of the path. However, the module will not be loaded

require.resolve('./testModule.js')

require.cache object: represents the cache area that caches all loaded modules

console.log(require.cache)

You can access a module through name contention

require.cache['模块文件名']

Recommended learning: "nodejs video tutorial"

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