What are the js data type conversions? Summary of methods for js data type conversion

What this article brings to you is about js data type conversion? A summary of js data type conversion methods has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

In js, data type conversion is divided into explicit data type conversion and implicit data type conversion.
JavaScript data types are divided into six types, namely null, undefined, boolean, string, number, and object.
Object is a reference type, and the other five are basic types or primitive types. We can use the typeof method to print
to find out which type something belongs to. To compare variables of different types, you must first convert the type, which is called type conversion.
Type conversion is also called implicit conversion. Implicit conversions usually occur with the operators addition, subtraction, multiplication, division, equals, and less than, greater than, etc. .

1. js explicit data type conversion

1.1 Convert to number (Number type)

1) Number conversion

var a = '123';
a = Number(a);

• If the converted content itself is a numerical string, it will return itself during future conversions.

• If the converted content itself is not a numerical string, the result will be NaN during conversion.

• If the content to be converted is an empty string, the result of the conversion is 0.

• If it is other characters, the result will be NaN during future conversion.

2) parseInt()

var a = '123';
a =  parseInt(a);

• Ignore the spaces in front of the string until the first non-empty character is found, and the number will also be The following non-numeric strings are removed.

• If the first character is not a numeric sign or a negative sign, NaN is returned.

• will round decimals. (Round down)

3) parseFloat();//Floating point number (decimal)

Same as parseInt, the only difference is that parseFloat can retain decimals.

1.2 Convert to string (String)

1) String()

var a = 123;a = String(a);

2) toString() method to convert (packaging class)

var a = 123; a = a.toString();undefined，null不能用toString。

1.3 Convert to boolean type

var a ='true'; a = Boolean(a);

Note: When performing boolean conversion, all contents will result in true after conversion,
Except: false, "" (empty string), 0, NaN , undefined.

2. js implicit data type conversion

2.1 Convert to Number

var a = '123';a=+a;

Addition, subtraction, multiplication, division and the remainder can implicitly convert a string into a number.

2.2 Convert to string

var a = 123;a = a + '';

2.3 Convert to boolean

var a = 123;a = !!a;

3. Data type conversion between js value types

3.1 Use operations on numbers and strings

If operators are used to operate numbers and strings, the numbers will be converted to strings first, and then
string concatenation operations will be performed:

var text = 'asd';var num = 123;
alert(text+num);

3.2 Boolean values ​​involved Operator operation

If there is a Boolean type involved, the Boolean value will first be converted into the corresponding number or string, and then the corresponding
string connection or arithmetic operation will be performed.

var bool = true;var num = 8;
console.log(bool + num);

The above code first converts true to the number 1, and then performs arithmetic addition.

var bool = true;var num = "8";
console.log(bool + num);

The above Boolean value will be converted into the corresponding string form "true", and then string concatenation is performed.

3.3 Subtraction operation

If a subtraction operation is performed, both operands will be converted into numbers first, and then arithmetic operations will be performed.

var bool = true;var num = "8";
console.log(bool - num)

true will be converted to the number 1, the string "8" will be converted to the number 8, and then arithmetic operations will be performed.
The same applies to conversions of multiplication, division, greater than, less than and subtraction.

3.4 ==Equality operation

undefined and null are special, both of them use == The operator return value is true.

console.log(undefined==null);

When comparing other value types, the operands will be converted into numbers

console.log("3"==3);

The above code will convert the string "3" into a number and then compare.

console.log("1"==true);

The above code will convert "1" and true into numbers respectively, and then compare them.

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