What are the three types of casts in JavaScript?
The three forced type conversions are: 1. Conversion to numeric type, Number(), parseInt(), parseFloat(); 2. Conversion to string type, toString(), String(); 3. Convert to Boolean type, Boolean().
The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.
JavaScript is a weakly typed language, and its value data type can be changed.
Some languages require specifying the data type of each variable. Such a language is called a strongly typed language, such as java C
Forced type conversion
There are two types of type conversion: one One is explicit conversion, which requires programmers to manually write code conversion; the other is implicit conversion, which is converted by the JavaScript interpreter.
JavaScript provides the following functions for explicit conversion:
1. Convert to numeric type: Number(mix), parseInt(string,radix), parseFloat(string)
2. Convert to string type: toString(radix), String(mix)
3. Convert to Boolean type: Boolean(mix)
Convert to numeric type
Number(mix) function
Number(mix) function can convert any type of parameter mix into a numerical type. The rules are:
1. If it is a Boolean value, true and false are converted to 1 and 0 respectively
2. If it is a numeric value, it returns itself.
3. If it is null, return 0
4. If it is undefined, return NaN.
5. If it is a string, follow the following rules:
a. If the string only contains numbers, convert it to decimal (ignoring the leading 0)
b. If the string contains a valid floating point format, convert it to a floating point value (ignoring the leading 0)
c. If it is an empty string, convert it to 0
d. If the string contains a format other than the above, convert it to NaN
6. If it is an object, call the valueOf() method of the object, and then convert the returned value according to the previous rules. If the result of the conversion is NaN, call the object's toString() method and convert the returned string value again according to the previous rules.
Example
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>数据类型转换</title>
</head>
<body>
<script>
println(Number(false));
println(Number(true));
println(Number(123));
println(Number(null));
println(Number(undefined));
println(Number(person));
function println(a){
document.write(a+'<br>');
}
var person={};//字面量创建对象
// 设置字面量对象属性
person.name='huangshiren';
person.age=58;
person.appetite=3;
person.eat=function(){
document.write('正在吃饭');
}
</script>
</body>
</html>parseInt(string, radix) function
Parameter description:
string The value to be parsed. If the argument is not a string, it is converted to a string (using the ToString abstract operation). Whitespace characters at the beginning of the string will be ignored.
radix An integer between 2 and 36 (the basis of mathematical systems) that represents the radix of the above string. For example, the parameter "10" means using the decimal numerical system we usually use. Always specifying this parameter eliminates confusion when reading this code and ensures that the conversion results are predictable. Different implementations produce different results when the base is not specified, usually defaulting to 10.
parseInt(string, radix) function converts a string into an integer type value. It also has certain rules:
1. Ignore spaces in front of the string until the first non-empty character is found
2. If the first character is not a numeric sign or a negative sign, return NaN
3. If the first character is a number, continue parsing until the string is parsed or a non-numeric symbol is encountered.
4. If the result of the previous step starts with 0 , it will be parsed as octal; if it starts with x, it will be parsed as hexadecimal
5. If the radix parameter is specified, radix will be used as the base for parsing
Example
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>数据类型转换</title>
</head>
<body>
<script>
println(parseInt("12.34567",10));
println(parseInt("de",10));
println(parseInt("0123456789",10));
println(parseInt("0e0",16));
println(parseInt("0101010001",2));
function println(a){
document.write(a+'<br>');
}
</script>
</body>
</html>parseFloat(string) function
parseFloat(string) function converts a string into a floating point type value.
Its rules are basically the same as parseInt, but there are some differences: the first decimal point symbol in the string is valid, and parseFloat will ignore all leading 0s. If the string contains a number that can be parsed as an integer , returns an integer value instead of a floating point value.
Example
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>数据类型转换</title>
</head>
<body>
<script>
println(parseFloat("3.14"));
println(parseFloat("314e-2"));
println(parseFloat("0.0314E+2"));
println(parseFloat("3.14more non-digit characters"));
function println(a){
document.write(a+'<br>');
}
</script>
</body>
</html>Convert to string type
toString(radix) method. All types of values except undefined and null have a toString() method, which returns a string representation of the object.
Example
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>数据类型转换</title>
</head>
<body>
<script>
var count=10;
println(count.toString());
var boolean=true;
println(boolean.toString());
var today=new Date();
println(today.toString());
var shoppingCart=['鞋','连衣裙','皮带'];
println(shoppingCart.toString());
var person={};//字面量创建对象
// 设置字面量对象属性
person.name='huangshiren';
person.age=58;
person.appetite=3;
person.eat=function(){
document.write('正在吃饭');
}
println(person.toString());
function println(a){
document.write(a+'<br>');
}
</script>
</body>
</html>Convert to Boolean type
Boolean(mix) function converts any type of value to a Boolean value.
Example
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>数据类型转换</title>
</head>
<body>
<script>
var count=10;
println(Boolean(count));
println(Boolean(0));
println(Boolean(4<3));
println(Boolean(null));
println(Boolean(""));
println(Boolean(undefined));
var shoppingCart=['鞋','连衣裙','皮带'];
println(Boolean(shoppingCart));
var person={};//字面量创建对象
// 设置字面量对象属性
person.name='huangshiren';
person.age=58;
person.appetite=3;
person.eat=function(){
document.write('正在吃饭');
}
println(Boolean(person));
function println(a){
document.write(a+'<br>');
}
</script>
</body>
</html>[Recommended learning: javascript advanced tutorial]
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