Need for having Eval function in javascript

Javascript has function called
eval() which evaluates a string and executes it as if it was script code.

Let us see the need for having this eval function.

Consider the below sample code in javascript.

document.myform.category_name1.value=””;
document.myform.category_name2.value=””;
document.myform.category_name3.value=””;
category_name1,category_name2,category_name3.....which are dynamic in a page.
suppose we want to achieve above three statements in a for loop

for(i=1;i<=3;i++)
{
 var category_name=“category_name”+i;
 document.myform.category_name.value=””;
}
Trying above way, does not work.

Trying following way, will work well.
for(i=1;i<=3;i++)
{
 category_name=”category_name”+i;
 temp="myform."+category_name;
        clear=temp+'.value="";' ;
        eval(clear); 
}

We can refer this article to know more about eval.

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