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eval is an important function as it allows you build Javascript dynamically
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For instance document.forms[0].actualtextname.value is value of form element specified as
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<INPUT TYPE="text" NAME="actualtextname" VALUE="value" onChange="handle(this.name)" >
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this.name holds actualtextname but as an ascii string which cannot be directly be used in
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var x = document.forms[0].actualtextname.value;
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var x = eval("document.forms[0]." + actualtextname + ".value"); // works!
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eval applies JavaScript interpreter to argument and then re-interprets as shown above
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This can be used to copy information between forms as in
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eval("document.forms[1]." + actualtextname + ".defaultvalue") = eval("document.forms[0]." + actualtextname + ".value")
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eval did not work properly for a long time! -- Please check on your browser
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Addon