Relevant introduction to the array function array() in JavaScript

The importance of arrays in programming languages ​​is self-evident. Arrays in JavaScript are also one of the most commonly used objects. Arrays are ordered collections of values. Due to weak types, arrays in JavaScript are very flexible. , powerful. Unlike Java and other strongly typed high-level languages, arrays can only store elements of the same type or its subtypes. JavaScript can store multiple types of elements in the same array, and the length can also be dynamically adjusted. Increasing or decreasing data automatically changes the length of the array.

Array() is a built-in constructor function used to construct an array. Arrays are mainly created in the following three ways:

<span class="pln">array </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Array</span><span class="pun">()</span><br/><span class="pln">array </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Array</span><span class="pun">([</span><span class="pln">size</span><span class="pun">])</span><span class="pln">array </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Array</span><span class="pun">(</span><span class="pln">element0</span><span class="pun">,</span><span class="pln"> element1</span><span class="pun">,</span><span class="pln"> </span><span class="pun">...,</span><span class="pln"> elementN</span><span class="pun">)</span>

Parameters

Parameter size is the expected number of array elements. In the returned array, the length field will be set to the value of size.

Parameter element ..., elementn is the parameter list. When the constructor Array() is called with these arguments, the elements of the newly created array are initialized to these values. Its length field will also be set to the number of parameters.

Return value

Returns the newly created and initialized array.

If no parameters are used when calling the constructor Array(), the returned array will be empty and the length field will be 0.

When you call the constructor and only pass it a numeric parameter, the constructor will return an array with the specified number of elements and undefined.

When Array() is called with other parameters, the constructor will initialize the array with the value specified by the parameter.

When the constructor is called as a function without using the new operator, it behaves exactly the same as when it is called with the new operator.

Array object method

Array object property

concat() method:

Combined array

[1,2]concat([3,4],[5,6]);//[1,2,3,4,5,6]

join() method:

<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><br/><span class="pln"> </span><span class="kwd">var</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">,</span><span class="lit">2</span><span class="pun">,</span><span class="lit">3</span><span class="pun">];</span><br/><span class="pln"> a</span><span class="pun">.</span><span class="pln">join</span><span class="pun">(</span><span class="str">""</span><span class="pun">);</span><span class="com">// =>"123"</span><span class="tag"></script></span>

pop() method:

Remove array The last element and returns it

<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><br/><span class="pln"> </span><span class="kwd">var</span><span class="pln"> fruits </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="str">"apple"</span><span class="pun">,</span><span class="str">"banana"</span><span class="pun">,</span><span class="str">"pineapple"</span><span class="pun">];</span><br/><span class="pln"> fruits</span><span class="pun">.</span><span class="pln">pop</span><span class="pun">();</span><span class="com">// pineapple </span><br/><span class="pln"> console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">fruits</span><span class="pun">);</span><span class="com">//["apple","banana"]</span><span class="tag"></script></span>

shift() method:

Removes and returns the first element of the array.

<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><br/><span class="pln"> </span><span class="kwd">var</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">,</span><span class="lit">2</span><span class="pun">,</span><span class="lit">3</span><span class="pun">];</span><br/><span class="pln"> a</span><span class="pun">.</span><span class="pln">shift</span><span class="pun">();</span><span class="com">//1</span><br/><span class="pln"> console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">a</span><span class="pun">);</span><span class="com">//[2,3]</span><span class="tag"></script></span>

slice(start,end)

Method: intercept a certain part of the array without any modification to the original array.

<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><br/><span class="pln">  </span><span class="kwd">var</span><span class="pln"> num </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="str">"a"</span><span class="pun">,</span><span class="str">"b"</span><span class="pun">,</span><span class="str">"c"</span><span class="pun">,</span><span class="str">"d"</span><span class="pun">,</span><span class="str">"e"</span><span class="pun">];</span><br/><span class="pln">  console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">num</span><span class="pun">.</span><span class="pln">slice</span><span class="pun">(</span><span class="lit">1</span><span class="pun">,</span><span class="lit">4</span><span class="pun">));</span><span class="com">//["b","c","d"]</span><br/><span class="pln">  console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">num</span><span class="pun">);</span><span class="com">//["a","b","c","d","e"]</span><span class="tag"></script></span>

splice(start,delete_count,i1,i2...)

Method: Delete array elements and add new elements at the same time. i1 and i2 are the new elements to be inserted

<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><br/><span class="pln"> </span><span class="kwd">var</span><span class="pln"> arr </span><span class="pun">=</span><span class="pln"> </span><span class="pun">[</span><span class="str">"js"</span><span class="pun">,</span><span class="str">"css"</span><span class="pun">,</span><span class="str">"html"</span><span class="pun">,</span><span class="str">"php"</span><span class="pun">,</span><span class="str">"c"</span><span class="pun">];</span><br/><span class="pln"> arr</span><span class="pun">.</span><span class="pln">splice</span><span class="pun">(</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="str">"python"</span><span class="pun">,</span><span class="str">"jquery"</span><span class="pun">);</span><span class="com">//["css","html"]</span><br/><span class="pln"> console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">arr</span><span class="pun">);</span><span class="com">//["js","python","jquery""php","c"]</span><span class="tag"></script</span>

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