Tech Junkie Blog - Real World Tutorials, Happy Coding!: JavaScript : The eval() Function

Friday, November 5, 2021

JavaScript : The eval() Function

The eval() function in JavaScript provides the power of dynamic evaluation, it evaluates a strings of JavaScript codes and returns a value.  If you use the eval on pair of string numbers it will be forgiving and give you the number if it can.  For example if you type int

eval("4+5")  the result will be 9 even though it's a string

Just because you can evaluate numbers that are strings, are you supposed to do it?  It's something you have to consider carefully before you go down that path.

The eval() function takes a one argument a string.  It tries to parse the argument as JavaScript code, if it fails a SyntaxError is thrown.  If it is successful then a value is returned or an undefined is returned if there are no value.  Since eval() uses a lot of interpretation of the code performance can take a hit.

For example if you type in the following code you will get an undefined and a SyntaxError


var myvar = "my variable";



  1. How to Get Free washer and dryer for low income Families
    Securing essential appliances like a washer and dryer can be a financial challenge for many low-income families. It's heartening to see initiatives that aim to bridge this gap and provide much-needed support.

  2. There are budgeting apps that can help single moms streamline their finances and gain better control over their money. Read more

  3. Single motherhood can be both rewarding and challenging. Many single moms are the primary breadwinners for their families, juggling multiple responsibilities, and often facing financial constraints. Know more


Search This Blog