Sonar Plugins

Rule: Declare variables before usage

Details

  • Type: New Feature New Feature
  • Status: Closed Closed
  • Priority: Major Major
  • Resolution: Fixed
  • Affects Version/s: None
  • Fix Version/s: JAVASCRIPT-1.3
  • Component/s: JavaScript
  • Labels:
    None
  • Number of attachments :
    0

Description

Compare:

var x = 1;

function fun() {
  print(x); // undefined
  if (false) {
    var x = 42;
  }
}

fun();

and

var x = 1;

function fun() {
  print(x); // 1
  if (false) {
    x = 42;
  }
}

fun();

See

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Freddy Mallet added a comment - - edited

*Description:
One of the sources of most confusion for JavaScript beginners is scoping. The reason scoping is so confusing in JavaScript is because it looks like a C-family language but doesn't behave the same way. Indeed C, and the rest of the C family, has block-level scope. When control enters a block, such as an if statement, new variables can be declared within that scope, without affecting the outer scope. This is not the case in JavaScript where only functions create a new scope.

The following code snippet illustrates this rule:

var x = 1;

function fun(){
  print(x); // Non-Compliant as x is declared later in the same scope
  if(something) {
    var x = 42; // declaration
  }
}

fun();  //Unexpectedly Print 42 and not 1

Whereas the following code snippet is correct:

var x = 1;

function fun() {
  print(x); // 1
  if (something) {
    x = 42;
  }
}

fun(); //Print 1
Show
Freddy Mallet added a comment - - edited *Description: One of the sources of most confusion for JavaScript beginners is scoping. The reason scoping is so confusing in JavaScript is because it looks like a C-family language but doesn't behave the same way. Indeed C, and the rest of the C family, has block-level scope. When control enters a block, such as an if statement, new variables can be declared within that scope, without affecting the outer scope. This is not the case in JavaScript where only functions create a new scope. The following code snippet illustrates this rule: var x = 1; function fun(){ print(x); // Non-Compliant as x is declared later in the same scope if (something) { var x = 42; // declaration } } fun(); //Unexpectedly Print 42 and not 1 Whereas the following code snippet is correct: var x = 1; function fun() { print(x); // 1 if (something) { x = 42; } } fun(); //Print 1
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Evgeny Mandrikov added a comment -

Done.

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Evgeny Mandrikov added a comment - Done.
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Freddy Mallet added a comment -

Sorry to reopen this ticket @Evgeny, the description still needed to be improved.

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Freddy Mallet added a comment - Sorry to reopen this ticket @Evgeny, the description still needed to be improved.
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Evgeny Mandrikov added a comment -

Done.

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Evgeny Mandrikov added a comment - Done.
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Freddy Mallet added a comment -

Manually tested !

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Freddy Mallet added a comment - Manually tested !

People

  • Assignee:
    Evgeny Mandrikov
    Reporter:
    Evgeny Mandrikov
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Dates

  • Created:
    Updated:
    Resolved: