How to force conversion of numerical values ​​in javascript? (Method summary)

The content of this article is about how to force conversion of numerical values ​​in javascript? (Method summary) has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Javascript data types are divided into basic data types and reference data types

Basic data: Number, Boolean, Undefined, Null, String;

Reference data: Object;

When 0.000...01, when the decimal point is greater than or equal to 7 digits, it will be automatically converted to scientific notation

When 20000...00, when the integer part is greater than or equal to 22 digits, it will be automatically converted into Scientific notation.

Number(x): one parameter;

• When the parameter is Number type: it can be output correctly;

console.log(Number(1));        //1
console.log(Number(1e-7));    //1e-7
console.log(Number(0b111));  //7
console.log(Number(NaN));   //NaN

• When the parameter is Boolean type: true->1;fasle->0;

console.log(Number(true));  //1
console.log(Number(false)); //0

• When the parameter is undefined: its value is NaN

console.log(Number(undefined)); //NaN

• When the parameter is null:

console.log(Number(null));    //0

• When the parameter is String type:

//数字字符串
console.log(Number("123"));   //123
console.log(Number("-123"));  //-123
console.log(Number("12.3"));  //12.3
console.log(Number("1e-7"));  //1e-7
console.log(Number("0xff"));  //255
console.log(Number("00123")); //123    
console.log(Number("   123")); //123
console.log(Number("\t\n123")); //123

//数字+字符或全字符字符串
console.log(Number('a123'));  //NaN
console.log(Number("false")); //NaN
console.log(Number("a123"));  //NaN

//空串或者空格字符串
console.log(Number("\t\n"));   //0
console.log(Number("  "));     //0
console.log(Number(""));       //0

• When the parameter type is an object: perform .valueOf() first, and if the object is obtained, perform toString() until the basic data type is obtained. For example {}.valueOf().toString() = "[object Object]" The final number result is NaN

console.log(Number({}));  //NaN
console.log(Number([1])); //1
console.log(Number([1,2]));  //NaN
cosole.log(Number([]));    //0

parseInt(x,y): 2 parameters,

The process is: first convert String(x) into a string, and then convert the value into a decimal number using the y base as the base. If not filled in, it will be 10. The range of y: [2,36]

When there is no parameter y:

• When the x parameter is number: It is worth noting that values ​​of type 0.001, 1e-7 will be rounded off after the decimal point (e) The value of , returns the previous one.

console.log(parseInt(123));   //123
console.log(parseInt(1e-7));  //1
console.log(parseInt(0xff));  //255
console.log(parseInt(NaN));   //NaN
console.log(parseInt(0.00001)); //0

• x parameter is boolean, undefined, null:

console.log(parseInt(true));  //NaN
console.log(parseInt(false)); //NaN
console.log(parseInt(undefined)); //NaN
console.log(parseInt(null));    //NaN

• x parameter When it is a String type: You need to pay attention to the space-time string, space string, and numeric characters

console.log(parseInt(""));   //NaN
console.log(parseInt("-123"));  //-123
console.log(parseInt("  "));  //NaN
console.log(parseInt("\t\n"));   //NaN
console.log(parseInt("a123")); //NaN
console.log(parseInt("123a")); //123

• When the parameter x is an object: The same applies to .valueOf(), If the object is obtained, then perform toString() until the basic data type is obtained, and then output according to the above rules

console.log(parseInt({1:2}));   //"[object Object]"->NaN
console.log(parseInt([]));      //""->NaN
console.log(parseInt([1,2]));   //"1,2"->//1

• with parameters x, y, when When y is 0, null, undefined, or NaN, y will be ignored and defaulted to 10. If it exceeds the range of [2, 36], it will return NaN. When the x value can be expressed in y base, it will return NaN. The rest can be represented by as many numbers as possible. Several

console.log(parseInt("f",2));   //NaN
console.log(parseInt("11f",2);  //3
console.log(parseInt("123",37)); //NaN
console.log(parseInt("0xff",0));  //255
console.log(parseInt("0xff",NaN)); //255
console.log(parseInt("ff",[]));  //NaN

parseFloat(x): A parameter that can correctly represent floating point numbers and scientific notation, but cannot correctly represent string base numbers. The rest is the same as parseInt(x, 10) Same as

console.log(parseFloat(0xff));  //255
console.log(parseFloat("0xff"));  //0  
console.log(parseInt("0xff"));   //255  个人猜测parseInt(x,y)有y的存在所以能正确输出
console.log(parseFloat(1e22));   //1e22
console.log(parseFloat(1e-7));   //1e-7
console.log(parseFloat("00123"));  //123
console.log(parseFloat(" "));     //NaN

String(), .toString()

• First: undefined, null has no toString() attribute and can only pass String(undefiend)

• Second: y.toString(x), which means to convert the target value y into an x-based value

console.log(String(null));  //"null"
console.log(0xff.toString(2));  //"11111111"
console.log(oxff.toString()); //"255" 不填默认10进制

The above is the detailed content of How to force conversion of numerical values ​​in javascript? (Method summary). For more information, please follow other related articles on the PHP Chinese website!