Functions or variables should not be redeclared

  • Code Quality
  • Medium, Low
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This rule applies when a function or a variable is redeclared in local context.

In JavaScript, it is possible to redefine the function and only the last one is used. This causes confusion as to where the function is actually defined.

Since functions and variables are hoisted in JavaScript, redeclared variables combined with hoisting and function-scoped var cause confusion as to where the variable is defined.

function foo() {
    var code = 1;
    if (true) {
        var code = 2;
    console.log(code); // code has a value of 2 because 'var' is not block-scoped

Note: This rule applies only for the variable whose name is length of 3 characters or above. It is because short variable name, e.g. i, is frequently used as loop counters.

Noncompliant Code Example

function a() { return 1; }
function a(b) { return b; } // DUPLICATE_DECL alarm

var foo;
var foo; // DUPLICATE_DECL alarm

Compliant Code Example

// Choose the function which you intend to apply. And delete others.
function a(b) { return b; }

// Delete duplicated one
var foo;


This rule was introduced in DeepScan 1.0.0-alpha.