Detailed explanation of how jQuery determines the type and size of uploaded images

This time I will bring youjQueryDetailed explanation of the method of judging uploadedpicturestype and size. What are theprecautionsfor jQuery to judge the type and size of uploaded pictures? The following is a practical case, let’s take a look.

JQuery is used here to determine the type and size of the uploaded image:

    
  
  
 
图片格式为：
 
图片大小为：
    

lastIndexOf()method retrieves the specifiedstringfrom back to front, if If the specified character appears, the position of the character is returned. If not, -1 is returned, and the position is counted from 0.

toUpperCase()method converts to uppercase letters

substring()method intercepts a string. The first parameter is the starting position, and the second parameter is the ending position (if omitted, the end of the string will be intercepted by default), and # The difference between ##slice()andsubstr()is thatsubstring()does not accept negative parameters

slice()The method is the same as thesubstring()method, the difference is that it accepts negative parameters (if the parameter is a negative number, the position is calculated from the end of the string)

substr()Method to intercept a string, the first parameter is the starting position, the second parameter is the intercepted length (different from slice and substring), it is no longer recommended to use

What are the main APIs of jQuery

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