JavaScript common function built-in methods

JavaScript is a scripting language used for web development and back-end development. Compared with other programming languages, JavaScript has a unique feature, that is, it has many practical functions and methods built into its core, which can make development easier. Here we take a look at the commonly used built-in functions of JavaScript.

1. alert()

alert() The function can pop up an alert box to display a message to the user. The syntax is as follows:

alert(message)

where the message parameter is the message string to be displayed.

2. prompt()

prompt() The function can pop up a prompt box to ask the user for input. The syntax is as follows:

prompt(message, defaultText)

The message parameter is the prompt message string to be displayed, and defaultText is the default input text.

3. confirm()

confirm() The function can pop up a confirmation box to confirm to the user whether to execute a certain operation. The syntax is as follows:

confirm(message)

where the message parameter is the confirmation message string to be displayed. When the user clicks the "OK" button, the confirm() function returns true, and when the user clicks the "Cancel" button, it returns false.

4. setTimeout()

setTimeout() The function can execute the specified function after the specified time. The syntax is as follows:

setTimeout(function, milliseconds)

where the function parameter is the function to be executed, and the milliseconds parameter is the number of milliseconds to delay.

For example, if you want to pop up a warning box after 3 seconds, you can write like this:

setTimeout(function() {
    alert("3秒已经过去了！");
}, 3000);

5. setInterval()

setInterval() The function can execute the specified function cyclically according to the specified time interval. The syntax is as follows:

setInterval(function, milliseconds)

where the function parameter is the function to be executed, and the milliseconds parameter is the number of milliseconds between loops.

For example, if you want to pop up a warning box every second, you can write:

setInterval(function() {
    alert("1秒已经过去了！");
}, 1000);

6. parseInt()

parseInt() The function can convert a string into an integer. The syntax is as follows:

parseInt(string, radix)

Among them, the string parameter is the string to be converted, and the radix parameter is a base number, which can be left blank. The default is decimal.

For example, if you want to convert the string "100" to an integer, you can write like this:

var num = parseInt("100");

7. parseFloat()

parseFloat() The function can convert a string to a floating point number. The syntax is as follows:

parseFloat(string)

where the string parameter is the string to be converted.

For example, if you want to convert the string "3.14" to a floating point number, you can write like this:

var num = parseFloat("3.14");

8. Number()

Number() The function can convert any type of value into a numeric value. The syntax is as follows:

Number(value)

where the value parameter is the value to be converted.

For example, if you want to convert the string "100" into a numerical value, you can write like this:

var num = Number("100");

9. toString()

toString() method can convert a numerical value into a string. The syntax is as follows:

num.toString()

where the num parameter is the value to be converted.

For example, if you want to convert the value 100 to a string, you can write:

var str = num.toString();

10. toFixed()

toFixed() method can retain the specified number of decimal places in a value. The syntax is as follows:

num.toFixed(digits)

The num parameter is the number of decimal places to be retained, and the digits parameter is the number of decimal places to be retained.

For example, if you want to keep the value 3.1415926 with 2 decimal places, you can write like this:

var num = 3.1415926;
var str = num.toFixed(2);

The above are some commonly used function built-in methods in JavaScript. Developers can follow Choose to use on demand.

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