How to convert JavaScript to numbers

Conversion method: 1. Use the conversion functions parseInt() and parseFloat(), the syntax "parseInt("value")" and "parseFloat("value")"; 2. Use forced type conversion, using Number () Convert the given value into a number, the syntax is "Number("value").

The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5 , Dell G3 computer.

The value obtained when js reads text box or other form data is of string type, for example, two text boxes a and b, if the value of a is 11, The value of b is 9, then a.value is smaller than b.value, because they are both in string form.

There are two main ways to convert JavaScript into numbers: conversion function and forced type conversion

1. Conversion function:

js provides two conversion functions: parseInt() and parseFloat(). The former Convert the value to an integer, which converts the value to a floating point number. Only by calling these methods on the String type can these two functions run correctly; for other types, they return NaN(Not a Number) .

Some examples are as follows:

parseInt("1234blue"); //returns 1234
parseInt("0xA"); //returns 10
parseInt("22.5"); //returns 22
parseInt("blue"); //returns NaN

The parseInt() method also has base mode, which can convert binary, octal, hexadecimal or any other base string into an integer. Base It is specified by the second parameter of the parseInt() method. An example is as follows:

parseInt("AF", 16); //returns 175
parseInt("10", 2); //returns 2
parseInt("10", 8); //returns 8
parseInt("10", 10); //returns 10

If the decimal number contains leading 0s, it is best to use base 10 so that you do not accidentally get an octal value. For example :

parseInt("010"); //returns 8
parseInt("010", 8); //returns 8
parseInt("010", 10); //returns 10

The parseFloat() method is processed similarly to the parseInt() method.

Another difference in using the parseFloat() method is that the string must represent a floating point number in decimal form , parseFloat() has no base mode.

The following is an example of using the parseFloat() method:

parseFloat("1234blue"); //returns 1234.0
parseFloat("0xA"); //returns NaN
parseFloat("22.5"); //returns 22.5
parseFloat("22.34.5"); //returns 22.34
parseFloat("0908"); //returns 908
parseFloat("blue"); //returns NaN

2. Forced type conversion

Also OK Use type casting to handle converting the type of a value. Using type casting allows you to access a specific value, even if it is of another type.

The 3 types of casts available in ECMAScript are as follows:

• Boolean(value)——Convert the given value to Boolean type;

• Number(value)——Convert the given value to Boolean type Convert the value to a number (can be an integer or a floating point number);

• String(value) - Convert the given value to a string.

Converting a value using one of these three functions will create a new value that stores the value directly converted from the original value. This can have unintended consequences.

The Boolean() function returns true when the value to be converted is a string, a non-zero number, or an object with at least one character (this will be discussed in the next section). If the value is an empty string, the number 0, undefined, or null, it will return false.

You can use the following code snippet to test Boolean type conversion.

Boolean(""); //false – empty string
Boolean("hi"); //true – non-empty string
Boolean(100); //true – non-zero number
Boolean(null); //false - null
Boolean(0); //false - zero
Boolean(new Object()); //true – object

Number()'s cast is similar to the parseInt() and parseFloat() methods, except that it converts the entire value instead of part of the value. The example is as follows:

Number(false) 0
Number(true) 1
Number(undefined) NaN
Number(null) 0
Number( "5.5 ") 5.5
Number( "56 ") 56
Number( "5.6.7 ") NaN
Number(new Object()) NaN
Number(100) 100

The last forced type conversion method, String(), is the simplest. The example is as follows:

var s1 = String(null); //"null"
var oNull = null;
var s2 = oNull.toString(); //won't work, causes an error

Recommended learning: javascript video tutorial

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