js split()[0]; js function with or without parentheses; jstypeof; js judgment array; js simple method of judging null and undefined

js split("-")[0]

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The difference between js with and without parentheses—
the difference between good js with and without parentheses—2 the
difference between js with and without parentheses—3 the
difference between js with and without parentheses—4
js with and without parentheses The Difference Between Brackets—5

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js typeof usage

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js remove string comma

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js judges whether it is an array

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A convenient way for js to judge undefined, null and empty strings
A convenient way for js to judge undefined, null and empty strings (the way to judge null values)

var a=XXX;
if(a){
    
    //如果a不为undefined和不为null和不为空串
  XXX
}