Question

i know this function gets a string of valid JavaScript expression or statements and evaluate the expression or execute the statements, but why we need to pass code to a function for execution instead of simply writing the code in the script?

Answer 1

Let’s say you have functions: makeCheckbox(), makeRadio() and makeSelect() (theoretically). You want to call function by user’s activity (for example menu click). You can make it with if, else if and so on, you can make switch, but you can eval too and make something like:

eval('make'+userChoose.charAt(0).toUpperCase()+string.slice(1)+'()');

where userChoose is one of the options: radio,checkbox or select, which is first-char-uppercased first and then concatenated with make (before) and () (after), which at the end calls one of the functions.

This is not good practice because in large projects you can’t simply find callings to function, because they’re “hidden behind” eval, but sometimes it’s the only way.