What is the javascript type conversion function?

JavaScript is a dynamic, weakly typed language. Type conversion is often required when operating and processing data. Due to its flexible nature, type conversion functions are very common in JavaScript. This article will introduce commonly used type conversion functions.

1. toString()

toString() function converts any type of value to string type and returns it as a string. For example:

var a = 123;
var b = true;
var c = null;

console.log(a.toString()); // 输出 "123"
console.log(b.toString()); // 输出 "true"
console.log(c.toString()); // TypeError: Cannot read property 'toString' of null

It should be noted that for values ​​of null and undefined types, calling the toString() function will report an error. Therefore, judgment needs to be made when performing type conversions on these two types of values.

2. parseInt()

parseInt() function converts a string type value to an integer type and returns it in integer form. For example:

var a = "123";
var b = "123.45";
var c = "abc";

console.log(parseInt(a)); // 输出 123
console.log(parseInt(b)); // 输出 123
console.log(parseInt(c)); // 输出 NaN

It should be noted that the parseInt() function will only parse the numeric part at the beginning of the string, and will stop when encountering non-numeric characters. Therefore, when using this function, you need to pay attention to the format of the string.

3. parseFloat()

parseFloat() function converts a string type value to a floating point type and returns it in floating point form. For example:

var a = "123.45";
var b = "abc";

console.log(parseFloat(a)); // 输出 123.45
console.log(parseFloat(b)); // 输出 NaN

Similar to the parseInt() function, the parseFloat() function will only parse the numeric part at the beginning of the string and will stop when encountering non-numeric characters.

4. Number()

Number() function converts any type of value to numeric type and returns it as a number. For example:

var a = "123";
var b = "123.45";
var c = true;
var d = false;
var e = null;

console.log(Number(a)); // 输出 123
console.log(Number(b)); // 输出 123.45
console.log(Number(c)); // 输出 1
console.log(Number(d)); // 输出 0
console.log(Number(e)); // 输出 0

It should be noted that for values ​​of null and undefined types, calling the Number() function will return 0. Additionally, when converting characters to numbers, NaN is returned if a non-numeric character is present.

5. String()

String() function converts any type of value to string type and returns it as a string. For example:

var a = 123;
var b = true;

console.log(String(a)); // 输出 "123"
console.log(String(b)); // 输出 "true"

It should be noted that for values ​​of null and undefined types, calling the String() function will return "null" and "undefined" strings.

Summary:

Type conversion is a very common operation in JavaScript, and the five type conversion functions are also more commonly used in practice. It should be noted that for different type conversion functions, when used in different scenarios, attention needs to be paid to type judgment and function applicability to avoid type conversion errors and program exceptions.

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