Synia Synia - 1 year ago 83
Node.js Question

In Express.js why does code after res.json() still execute?

In Node with Express, I have a piece of code like this.

if (req.body.var1 >= req.body.var2){
res.json({success: false, message: "End time must be AFTER start time"});
//other codes

I expected that if var1 is >= var2, the response would be sent and the execution would end. Like return statements in Java/C#

But appearantly that's not the case. After the response is sent, both 'Hi' and 'Hi2' and all the other code after that continues to get executed.

I was wondering how I would stop this from happening?

Also, I was wondering under what circumstances would you actually want code to keep on executing after a response has already been sent.


Answer Source

Express just calls a JavaScript function for the matched route. There's no special magic to know when the function is complete/incomplete. It just runs the function. However, it's very easy to exit the function whenever you want...

You can use return to stop executing the callback for a specific route in express. It's just JavaScript... the function will always attempt to run to completion'/some/route', (req, res)=> {
  if (req.body.var1 >= req.body.var2){
    // note the use of `return` here
    return res.json({success: false, message: "End time must be AFTER start time"});
    // this line will never get called
  // this code will only happen if the condition above is false
  //other codes

Warning about string comparsion

You're using

req.body.var1 >= req.body.var2

All HTML form values are sent to the server as strings.

// javascript string comparison
"4" > "3"  //=> true
"4" > "30" //=> true
parseInt("4", 10) > parseInt("30", 10) //=> false

I'm certain you'll need to make a more educated comparison than that. It looks like they're time values? So you'll likely want to convert those values to Date objects and do an accurate comparison.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download