About data type conversion in javascript

This article mainly introduces the conversion of data types in javascript, which has some reference value. Let's take a look at it below. 1. convert other data types to the number type.

Number ()-> strict

ParseFloat/parseInt-> non-strict

IsNaN (value) if the value is not of the numeric type, it first calls the Number to convert it to the numeric type and then determines whether it is a valid Number.

For example:

Number ("12px");-> NaN

ParseInt ("12px");-> 12

IsNaN ("12");-> false

Rule:

1) if the boolean type is converted to a number, true-> 1 false-> 0

2) convert null/undefined to the number null-> 0 undefined-> NaN 10 + null = 10 10 + undefined = NaN

3) to convert [] to a Number, first call the toString method of the array to []-> "", and then use the Number method to convert "-> 0

2. convert other data types to boolean ones.

Boolean

!!

! Convert to a boolean type first, and then

For example:

!! 1-> true

!! 0-> false

! []-> False !! []-> True

Rule:

Only the values 0, NaN, null, undefined, and "" are converted to the boolean type as false, and the other values are converted to true.

Special cases:

If your condition judgment only contains a single value, it first converts 1 to the Boolean Type (-> true) and determines whether it is true or false. If it is true, otherwise, the condition is invalid.

If (1) {} if ("3px" * 3) {//-> the condition is not true. "3px" * 3 = NaN-> false} if ("3px" + 3) {//-> condition is set to "3px" + 3 = "3 p x 3"-> true}

"+" In JS, it is not just a mathematical operation, but a String concatenation in case of a string

"-, *,/" Can only be mathematical operations in JS. If it is not a number type, it must be forcibly converted to a number for mathematical operations.

3. Compare the two values (==== compared, ==== compared data types are not converted by default). If the data types on the left and right sides are different, we need to follow a set of rules, convert the default data type

Value1 = value2

1) object = The object compares the memory address stored by itself. If the memory address is different, it is not equal [] = []-> false. Each empty array is a separate memory address.

2) object = string call toString method, convert the object to string [] = ""-> true

3) object = convert a Boolean object to a Number (toString-Number), and convert a Boolean object to a Number (true-> 1 false-> 0)

[] = False-> true []-> 0 false-> 0 0 = 0-> true

! [] = False->! [] Convert an empty array to a Boolean array first, and then convert it to the inverse type-> false = false-> true.

4) convert object = numeric object to numeric [] = 0-> true [] = 1-> false

5) both string = Boolean are converted to numbers "3" = true-> false "1" = true-> true

6) convert string = numeric string to numeric "" = 0-> true

7) Boolean = numeric Boolean to numeric true = 1-> true = 2-> false

8) null = undefined-> true null = undefined-> false

Null/undefined is not equal to any other value. null = 0-> false

9) NaN = NaN-> false NaN and any value (including itself) are not equal

The above is all the content of this article. I hope this article will help you in your study or work, and I also hope to support PHP!

For more information about data type conversion in javascript, refer to the PHP Chinese website!