How to convert string to number in javascript

Javascript method to convert a string into a number: 1. Use the parseInt() function to convert to an integer, or use the parseFloat() function to convert to a floating point number; 2. Use forced type conversion, the syntax "Number(value )", you can convert the given value into a number (integer or floating point number).

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

There are three main methods for converting strings to numbers in javascript

Conversion functions, forced type conversion, and weak type conversion using js variables.

1. Conversion function:

js provides two conversion functions: parseInt() and parseFloat(). The former converts the value to an integer, and the latter 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, NaN (Not a Number) is returned.

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 a base mode, which can convert binary, octal, hexadecimal or any other base string into an integer. The base is specified by the second parameter of the parseInt() method, as shown in the following example:

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 handled 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, and 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

[Recommended learning: js basic tutorial]

2. Forced type Conversion

You can also use type casting to handle the type of the converted value. Use a cast to access a specific value, even if it is of another type.

The three forced type conversions available in ECMAScript are as follows:

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

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

• String(value)——Convert the given value to Convert a given value into 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

3. Use js variable weak type conversion

Give me a small example, and you will understand after you look at it.

The code is as follows:

<script>
var str= &#39;012.345 &#39;;
var x = str-0;
x = x*1;
</script>

The above example takes advantage of the weak type characteristics of js and only performs arithmetic operations to achieve type conversion from string to number. However, this method is not recommended.

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