Javascript verifies the size of the uploaded image [client]

Source: Internet
Author: User

Requirement Analysis:
When uploading images, if you do not limit the size of the uploaded images, the consequences are very serious. So how can we solve a difficult problem? There are two methods:
1) background processing : Ajax post is submitted to the background, the image is uploaded to the server, and the image size is obtained for processing.
2) frontend handling : Use JavaScript to get the image size.
Obviously, the first method is not good. Because the file needs to be uploaded to the server first. If the file is large, the Internet access is not very fast. It takes a long time to fix the problem.
Function Analysis:
Here I will only introduce the different practices of IE and Firefox.
IE6:
Keyword: filesize onreadystatechange complete
In IE6, the file size can be obtained through the filesize attribute of the IMG object, but the correct value of this filesize attribute is created in the complete of the onreadystatechange event, that is CopyCode The Code is as follows: Onreadystatechange = "javascript: sizecheck (this);">
Function sizecheck (IMG ){

If (IMG. readystate = "complete "){
Alert (IMG. filesize );
}
}

Firefox3.0:
Keyword: getasdataurl () filesize
It is safe in Firefox. You cannot obtain the complete path of the uploaded image. You can only obtain the image name. However, the browser provides the nsidomfile interface, so you need to get the processed path through getasdataurl (), but this path does not affect the image SRC display.
Nsidomfile interface:
Domstring getasbinary ();
Domstring getasdataurl ();
Domstring getastext (in domstring encoding );Copy codeThe Code is as follows: <input type = "file" name = "uploadimg"
Onchange = "javascript: checkfilechange (this );"
Size = "12"/>
Function checkfilechange (OBJ ){
VaR IMG = Document. getelementbyid ("IMG ");
IMG. src = obj. Files [0]. getasdataurl ();
Alert (obj. Files [0]. filesize );
}

These are the processing methods of two different browsers. How can we combine them? I will post a small example below, in which I will use jquery to facilitate and obtain objects.Copy codeThe Code is as follows: <! Doctype HTML public "-// W3C // dtd xhtml 1.0 transitional // en" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<HTML xmlns = "http://www.w3.org/1999/xhtml" XML: lang = "ZH" lang = "ZH" dir = "LTR">
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = UTF-8"/>
<SCRIPT type = "text/JavaScript" src = "lib/jquery-1.3.2.min.js"> </SCRIPT>
<Title> check the size of the uploaded image </title>
<Style type = "text/CSS">
. IMG {width: 136px; Height: 102px ;}
. Imgerror {border: 3px solid red ;}
</Style>
<SCRIPT type = "text/JavaScript">
// Limit the size of the uploaded image to 100 KB
VaR maxsize = 100*1024;

// Image size limit information
VaR error_imgsize = "the image size cannot exceed 100 kb ";
// Default image
VaR nophoto = "IMGs/nophoto.gif ";

// Whether the image is qualified
VaR isimg = true;
/**
* Input file onchange event
* @ Params OBJ file object
* @ Return void
**/
Function checkfilechange (OBJ ){

// Initialization settings
$ (". Imgtable"). removeclass ("imgerror ");
Updatetips ("");
VaR IMG = $ (". IMG"). Get (0 );
Var file = obj. value;
VaR exp =/. \. jpg |. \. gif |. \. PNG |. \. BMP/I;
If (exp. Test (File) {// verify the format
If ($. browser. MSIE) {// determines if it is IE
IMG. src = file;
} Else {
IMG. src = obj. Files [0]. getasdataurl ();
Sizecheck (IMG );
}

} Else {
IMG. src = nophoto;
$ (". Imgtable"). addclass ("imgerror ");
Updatetips ("incorrect image format ");
Isimg = false;
}

}
/**
* Sizecheck check the image size
* @ Params IMG image object
* @ Return void
**/
Function sizecheck (IMG ){
// Initialization settings
$ (". Imgtable"). removeclass ("imgerror ");
Updatetips ("");
If ($. browser. MSIE) {// check whether it is IE
If (IMG. readystate = "complete "){
If (IMG. filesize> maxsize ){
$ (". Imgtable"). addclass ("imgerror ");
Updatetips (error_imgsize );
Isimg = false;
} Else {
Isimg = true;
}

} Else {
$ (". Imgtable"). addclass ("imgerror ");
Updatetips (error_imgsize );
Isimg = false;
}

} Else {
Var file = $ ("input: file [name = 'uploadimg ']") [0];

If (file. Files [0]. filesize> maxsize ){
$ (". Imgtable"). addclass ("imgerror ");
Updatetips (error_imgsize );
Isimg = false;
} Else {
Isimg = true;
}

}
}

/**
* Updatetips registration error message display
* @ Params STR display content
* @ Return void
**/
Function updatetips (STR ){
$ ("P # errortips"). Text (STR );
}
/**
* Commit registration submission
* @ Return void
**/
Function commit (){

VaR iscommit = true;
VaR usrname = $ ("input: Text [name = 'usrname']"),
Email = $ ("input: Text [name = 'email ']"),
IMG = $ (". IMG "),
File = $ ("input: file [name = 'uploadimg ']"),
FRM = Document. frm;

Iscommit = iscommit & isimg;

If (iscommit ){
FRM. Action = "about: blank ";
FRM. Submit ();
}
}
/**
* Errorimg image error display
* @ Params IMG image object
* @ Return void
**/
Function errorimg (IMG ){
IMG. src = nophoto;
}

</SCRIPT>
</Head>
<Body>
<Form name = "frm" method = "Post">
<P id = "errortips"> </P>
<Table cellpadding = "1" cellspacing = "0" width = "350px" border = "1">
<Tr>
<TD> <label> name: </label> </TD>
<TD> <input type = "text" name = "usrname" maxlength = "50"/> </TD>
</Tr>
<Tr>
<TD> <label> Gender: </label> </TD>
<TD> <input type = "radio" name = "sex" value = "0"/> male <input type = "radio" name = "sex" value = "0" /> female </TD>
</Tr>
<Tr>
<TD> <label> Email: </label> </TD>
<TD> <input type = "text" name = "email" maxlength = "100"/> </TD>
</Tr>
<Tr>
<TD> <lable> image </label> </TD>
<TD>
<Table cellpadding = "0" cellspacing = "0" class = "imgtable">
<Tr>
<TD> Onreadystatechange = "javascript: sizecheck (this);"/>
</TD>
</Tr>
<Tr>
<TD> <input type = "file" name = "uploadimg" onchange = "javascript: checkfilechange (this );"
Size = "12"/> </TD>
</Tr>
</Table>
</TD>
</Tr>
<Tr>
<TD colspan = "2"> <a href = "javascript: Commit ();" href = "javascript: Commit ();"> Registration </a> </TD>
</Tr>
</Table>
</Form>
</Body>
</Html>

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.