JS Basic Learning Notes (i)

JavaScript basics
1. Component: Consists of ECMAScript(translation, core, interpreter),DOM(ability to manipulate HTML),BOM(browser window), three parts.

Compatibility followed by [1. There are few compatibility issues, 2. Some operations are incompatible, 3. completely incompatible;]

2. Variable type: Numeric type (number) (string), Array (Arry), Boolean (Boolean),object (function), undefined (undefined) ; NaN (not present);

Type method for testing variables: alert (typeof)

Give me a chestnut:

var str= ' 1 '; if (typeof (Str) = = ' string ') {alert ("This is a variable of type string")); };

3. Type conversion: When converting a string, if the string does not contain a number, the program pops up nan! (Display type conversions, implicit type conversions)

One. Display Type conversions

①parseint: Converting a String type to a numeric type

Attributes (starting from left to right to detect numbers, the program automatically jumps out when a non-numeric type is encountered in the program; parseint can only be converted to integers)

var a=1.2; Alert (parseint (a)); Pop up 1

We now need a property that can completely convert the decimal!

②parsefload:hi to convert the decimals completely.

var b=1.2; Alert (Parsefload (b)); Pop up 1.2

Two. implicit conversion type

①==

Feature (the first step is to convert the variable types on both sides to the same type before comparing them)

var a=1;    var b= ' 1 ';    alert (A==B); The bounce is true.

②===

Attribute (the type of the variable on both sides of the conversion is started to compare)

var a=1;    var b= ' 1 ';    alert (A===B); The bounce is false.

4. NaN

Concept: nan is a numeric type, and any number and Nan are equal to Nan when added.

nan = =nan is unequal, only isNaN () can judge that Nan is equal to itself

Chestnuts:

is Small applications of Nan

JS Basic Learning Notes (i)