CODEWITHSUNDEEP
javascriptnode.jscallbacktry-catch
Anonymous
Anonymous

Reputation: 4630

How to prevent double callbacks during try...catch in javascript / nodejs?

Today I discovered an error in my code that leads to callbacks potentially being executed more than once. The intended usage of try...catch was meant for JSON.parse() operation; however, an error has occurred right after it inside the callback itself.

var body='{}';
var callback=function (arg){
    console.log('callback executed with arg='+arg);
    arg?    pack_michael(): pack_jolly();
}
try {
    JSON.parse(body); //if JSON parse successful should callback once with true argument
    callback(true);
} catch (e){
    callback(false);  //if JSON parse fails should callback once with false argument
}

Above code results in double callback printing this:

callback executed with arg=true
callback executed with arg=false

I can think of some ugly solutions like creating a variable and checking if an error has occurred or nesting another unnecessary try...catch, but isn't there any neat solution to deal with this?

Upvotes: 0

Views: 412

Answers (2)

bsekula
bsekula

Reputation: 919

Add new try/catch around callback 

try {
  JSON.parse(body);
  try {
    callback(true);
  } catch(err) { console.log("Error in callback")}
} catch (e){
  callback(false);  //if JSON parse fails should callback once with false argument
}

Upvotes: 0

CertainPerformance
CertainPerformance

Reputation: 371168

Call the callback after the try/catch:

let parseOk = false;
try {
    JSON.parse(body);
    parseOk = true;
} catch (e){
    // parseOk is already false
}
callback(parseOk);

If you also want to catch errors in the callback itself, you can surround it in a different try/catch, but that's separate from errors that occur in the JSON.parse, so they shouldn't be combined.

Upvotes: 4

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