Summary of JavaScript knowledge points: how to improve performance

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Summary of JavaScript knowledge points: how to improve performance_javascript skills

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May 16, 2016 pm 03:19 PM

JavaScript performance optimization

The performance issues of JavaScript cannot be underestimated, which requires us developers to pay more attention to some details when writing JavaScript programs. This article introduces the knowledge points of JavaScript performance optimization in great detail, which is definitely useful information.

Let me first consolidate the basic syntax of javascript:

Basic syntax of javascript

Use the var keyword to define variables

Syntax: var variable name=variable value

identifier: ①, composed of letters, numbers and underscores. It cannot start with a number. It cannot be a keyword. It is strictly case-sensitive

Data type:

Numeric type: number

String: string

Boolean type: boolean

Special data types: undefined empty undefined unassigned

Null value: null

Reference type object function

Detect the data type of the parameter: typeof() returns the string corresponding to the data type

Usage of two equal signs == and three equal signs ===

==: Comparison values are equal regardless of data type

===: Congruent comparison is related to both numerical values and data types

Boolean environment: automatically convert to Boolean value when encountering if

Boolean environment in string string: empty is false, non-empty is true

Boolean environment in numerical number: 0 is false, non-0 is true

The relationship between number and string

①. When encountering, perform splicing operation

②. When operations need to be performed, the string must be converted into a numerical value

Conversion method 1, string*1 into numeric type

Conversion method 2: Convert Number (string) to numeric type

1: Loading location of js files

In HTML files, <script> tags can be added to the <head> area and <body> area. In view of the single-threaded reason for JavaScript execution and UI rendering, if the js file is loaded, it will block the subsequent parsing process of the page. The page will wait until the js file is fully loaded and run before continuing to perform the operation. Then the problem arises, the page may be blank or stuck. As a front-end developer, it is important not only to realize the requirements, but also to provide a high-quality user experience. Then we need to eliminate the boring waiting of users. To solve this problem, here are two solutions that I have thought of: <br /> </script>

1. If the js file has no special requirements indicating that it needs to be loaded and compiled before the page is rendered, then choose to place the js file before the

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