How to type convert in javascript

Method: 1. Use the " " operator to automatically convert. 2. Use JS’s built-in functions for conversion. For example, toString() and String() can be converted into strings, Number() and parseInt() can be converted into numeric types, and Boolear() can be converted into Boolean types.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 5, Dell G3 computer.

1. Convert to string

1. Use toString method:

This method Not suitable for null and undefined, they have no toString method

        var  num = 18;
        var isRight = true;
        var a = null;
        console.log(num.toString());
        console.log(isRight.toString());

2. Use the String method:

This method is often used to convert null and undefined into string types

        console.log(String(num));
        console.log(String(isRight));
        console.log(String(a));

3. Splicing

        console.log(num+'');
        console.log(isRight+'');
        console.log(a+'');

2. Convert to numerical type

1 , Number method

Number method returns NaN as long as there is one letter in the string, and can convert boolean type

        var str1 = '123';
        var str = 'abc';
        var str2 = '123abc'
        var isRight = true;
        console.log(Number(str1));//值为123
        console.log(Number(str));//值为NaN(不是数值）
        console.log(Number(str2))//Number方法只要字符串中有一个字母则返回NaN
        console.log(Number(isRight));//值为1

2, parseInt method

The parseInt method converts a numeric value into a number in a string. If it encounters a non-number, it will return. The boolean type cannot be converted.

        console.log(parseInt(str1));//值为123
        console.log(parseInt(str));//值为NaN
        console.log(parseInt(str2));//parseInt方法在字符串中遇到数值转换成数字，如果遇到非数字就会返回

3, parseFloat method

Similar to parseInt, if there are only integers in the parsing, it will be parsed as integers

        console.log(parseFloat(str1));
        console.log(parseFloat(str));
        console.log(parseFloat(str2));
        console.log(parseFloat(isRight));//如果解析中只有整数则解析为整数

4, add ' ' or '-' method

Strings with letters cannot be converted, and boolean types can be converted:

"-" has a value and a string. First convert the string into a value, and then subtract. If the value conversion fails, it will be NaN

" "One side is a value and the other is a string, first convert the value into a string, and then concatenate it

        console.log(+str1);
        console.log(-str1);
        console.log(+str2);//不能转换有字母的字符串
        console.log(+isRight);//值为1
        console.log(str1-0);//值为123

3. Convert to Boolear type

1. Use Boolear method:

Five cases of conversion to false: null undefined ''(empty string) 0 NaN

        var str = 'abc';
        var num = 123;
        var a = null;
        var b;
        console.log(Boolean(str));
        console.log(Boolean(num));
        console.log(Boolean(a));
        console.log(Boolean(b));

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