Unexpected global variable declaration should be avoided

• UNEXPECTED_GLOBAL_DECL
• Code Quality
• Medium
• No tags

This rule applies when global variable is unexpectedly declared.

Assigning a value to undeclared variable creates a new variable inside the global scope. Unexpectedly created global variables can cause memory leaks.

For example, unexpected global variables can be created in the following cases:

1. Initialize a loop variable without declaration.
2. Assign to an intermediate variable accessed only inside a loop without declaration.
3. In the middle of variable declaration list, comma is missing or semicolon is inserted by mistake at the end of variable declaration.

Noncompliant Code Example

// Example 1
var b = [1, 2, 3];
for (a = 0 /* UNEXPECTED_GLOBAL_DECL alarm */; a < b.length; a++) {}

// Example 2
function foo(x) {
    for (var i = 0; i < x.length; i++) {
        bar = getBar(x[i]); // UNEXPECTED_GLOBAL_DECL alarm
        doSomething(bar);
    }
}

// Example 3
var c = 1,
    d = 2
    e = 3, // UNEXPECTED_GLOBAL_DECL alarm
    f = 4; // UNEXPECTED_GLOBAL_DECL alarm

Compliant Code Example

// Example 1
var b = [1, 2, 3];
for (var a = 0; a < b.length; a++) {}

// Example 2
function foo(x) {
    for (var i = 0; i < x.length; i++) {
        var bar = getBar(x[i]);
        doSomething(bar);
    }
}

// Example 3
var c = 1,
    d = 2,
    e = 3,
    f = 4;

Version

This rule was introduced in DeepScan 1.0.0-alpha.