Join method in JS

js Medium join Method
join Method is used to put all elements in an array into a string .

The elements are separated by the specified separator .

vernacular ：join Method can use different delimiters to construct this string .join Method value accepts a parameter , That is, the string used as the separator , Then return the string of all array items .

var arr = ["red","yellow","blue"];
var array = [];

Let's call join Method

1、

array = arr.join(undefined);
console.log(array);    


 The output is ： red,yellow,blue.

 because join Method parameters are not passed or passed undefined It will be separated by commas by default .

2、

array = arr.join("|");
console.log(array);   

 The output is ： red|yellow|blue.

join Parameter is used "|" To separate 
 

3、

array = arr.join(" | ");
console.log(array); 

 The output is ： red | yellow | blue.

join Parameters use " | " To separate , String is separated by whatever it is .   

4、

console.log(Array.isArray(array));  
console.log(typeof array);  

 The output is ：false   String

 If you use join To separate arrays , This variable will become a string type , Even if it was an array before, it will become a string type .

5、

console.log(array.join(" | "));

 Error in output result ： array.join is not a function

 because array Now it has become a string , and join Only arrays can be called , So wrong reporting ！