eval in javascript

1) eval is used to evaluate the expression.
Example:

var iValue =10;
document.write(eval(iValue+10));
eval("iFirst=10;iSecond=20;document.write(iFirst*iSecond)");

Output:
20
200

2) eval used to reduce the number of lines.

Suppose you are doing some validation part.
Without eval

if (document.myForm.Name.value.length==0)
{
alert("Name requires a value");
}

if (document.myForm.Salary.value.length==0)
{
alert("Salary requires a value");
}

Using eval

var fieldList = new Array('Name','Salary');
var tempObj;

for (count=0;count<fieldList.length;count++)
{
tempObj=EVAL("document.myForm." + fieldList[i]);
if (tempObj.value.length==0)
{
alert(fieldList[i] + " requires a value");
}
}

3) eval can be used to generate dynamic variable.

eval("iValue" + iIndex);
Same way we can use window["iValue"+ iIndex]