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eval is an important function that lets you evaluate JavaScript code on-the-fly
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For instance, document.forms[0].myName.value is the value of a form element:
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<INPUT TYPE="text" NAME="myName" VALUE="value" onChange="handle(this.name)">
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this.name holds myName as an ASCII string:
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var x = document.forms[0].myName.value; // No!
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var s = "document.forms[0]." + myName + ".value";
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var x = eval(s); // Yes!
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That is, eval applies the JavaScript interpreter to its argument
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This can be used to copy information between forms as in
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eval("document.forms[1]." + myName + ".defaultvalue")
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= eval("document.forms[0]." + myName + ".value")
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For a long time, eval didn't work right, so check your browser!
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