Does javascript have anything like a try catch?

Question

I have the following class:

var a = $scope.option.userMap[userId].name;

This fails when there is no value in userMap that has a key of userId. The error message comes up when it tries to do the .name of something that's not defined.

Is there a simple way that I could catch this error? When the error happens I would like the variable a to be set to "unknown"

Did you tried Google First? - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch — Mr. Alien, Jan 24 '14 at 15:34
This question appears to be off-topic because it could have been solved by taking a look at the language's documentation. — Cerbrus, Jan 24 '14 at 15:37

Alex · Answer 1 · 2014-12-23T10:18:12.697

Yes.

try {
    var a = $scope.option.userMap[userId].name;
} catch(e) {
    //catch a error
} finally {
    //execute always
}

About finally block vs return statement:

function something() {
    try {
        return $scope.option.userMap[userId].name;
    } catch(e) {
        return e.message
    } finally {
        alert('Yohoooo!')
    }
}

You will always see the alert when call the something function.

score 2 · Accepted Answer · answered Jan 24 '14 at 15:34

2

Javascript has something exactly like try / catch, but why use it when you can just check if the key exists instead :

if (userId in $scope.option.userMap) {

    var a = $scope.option.userMap[userId].name;

}else{

    var a = 'unknown';

}

answered Jan 24 '14 at 15:34

adeneo

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Very good, except `a` should be set to "unknown" :) – Jongware Jan 24 '14 at 15:36
1

@Jongware - Yeah, that's probably better ;-) – adeneo Jan 24 '14 at 15:36
1

+1, by the way, for answering the Question Not Asked: [Blindly using `try-catch` or checking your code for errors](http://stackoverflow.com/questions/3217294/javascript-try-catch-performance-vs-error-checking-code) – Jongware Jan 24 '14 at 15:40

score 1 · Answer 3 · answered Jan 24 '14 at 15:34

1

Of course:

try {
   // Live hard...dangerous code
} catch(e) {
   // Manage your mess
}

Optionall you can add a finally clause, that is always executed:

finally {
    // Always executed
}

answered Jan 24 '14 at 15:34

bgusach

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score 1 · Answer 4 · answered Jan 24 '14 at 15:35

1

Yes, there is.

This is the syntax:

try {
    //Run some code here
} catch(err) {
    //Handle errors here
}

For more information:

http://www.w3schools.com/js/js_errors.asp

answered Jan 24 '14 at 15:35

Denis C de Azevedo

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Download the plugin listed in my profile description – Mr. Alien Jan 24 '14 at 15:35

score 1 · Answer 5 · answered Jan 24 '14 at 15:39

Though the replies above have answered the question of whether JS has try/catch feature, they have failed to point out the fact that it is not best practice to use try/catch blocks to work around undefined variables. Better way to do this is:

var userObj = $scope.option.userMap[userId];
var a = userObj ? userObj.name : undefined;

Does javascript have anything like a try catch?

5 Answers5