Converting string to expression

Question

Is there any way to convert a string to an expression?

my string: var1 == null && var2 != 5

I want to use this string as a condition of the if(), Like if(var1 == null && var2 != 5)

Answer 1

One option is to create and call new Function:

var strExpr = "var1 == null && var2 != 5";
if (new Function("return " + strExpr)()) {
    // ...
}

Answer 2

Use eval. This will do

if (eval(" var1 == null && var2 != 5"))
{
}

Answer 3

To see how eval works, just write in console:

console.log(eval("1==1"));
console.log(eval("1==2"));

This will output true and false