Best Practices | PMD Source Code Analyzer

Rules which enforce generally accepted best practices.

Table of Contents

AvoidWithStatement

Since: PMD 5.0.1

Priority: High (1)

Avoid using with - it’s bad news

This rule is defined by the following XPath expression:

//WithStatement

Example(s):

with (object) {
    property = 3; // Might be on object, might be on window: who knows.
}

Use this rule by referencing it:

<rule ref="category/ecmascript/bestpractices.xml/AvoidWithStatement" />

ConsistentReturn

Since: PMD 5.0

Priority: Medium High (2)

ECMAScript does provide for return types on functions, and therefore there is no solid rule as to their usage. However, when a function does use returns they should all have a value, or all with no value. Mixed return usage is likely a bug, or at best poor style.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.ecmascript.rule.bestpractices.ConsistentReturnRule

Example(s):

// Ok
function foo() {
    if (condition1) {
        return true;
    }
    return false;
}

// Bad
function bar() {
    if (condition1) {
        return;
    }
    return false;
}

Use this rule by referencing it:

<rule ref="category/ecmascript/bestpractices.xml/ConsistentReturn" />

GlobalVariable

Since: PMD 5.0

Priority: High (1)

This rule helps to avoid using accidently global variables by simply missing the "var" declaration. Global variables can lead to side-effects that are hard to debug.

This rule is defined by the following XPath expression:

//Assignment[Name/@GlobalName = true()]

Example(s):

function(arg) {
    notDeclaredVariable = 1;    // this will create a global variable and trigger the rule

    var someVar = 1;            // this is a local variable, that's ok

    window.otherGlobal = 2;     // this will not trigger the rule, although it is a global variable.
}

Use this rule by referencing it:

<rule ref="category/ecmascript/bestpractices.xml/GlobalVariable" />

ScopeForInVariable

Since: PMD 5.0

Priority: High (1)

A for-in loop in which the variable name is not explicitly scoped to the enclosing scope with the ‘var’ keyword can refer to a variable in an enclosing scope outside the nearest enclosing scope. This will overwrite the existing value of the variable in the outer scope when the body of the for-in is evaluated. When the for-in loop has finished, the variable will contain the last value used in the for-in, and the original value from before the for-in loop will be gone. Since the for-in variable name is most likely intended to be a temporary name, it is better to explicitly scope the variable name to the nearest enclosing scope with ‘var’.

This rule is defined by the following XPath expression:

//ForInLoop[not(child::VariableDeclaration)]/Name[1]

Example(s):

// Ok
function foo() {
    var p = 'clean';
    function() {
        var obj = { dirty: 'dirty' };
        for (var p in obj) { // Use 'var' here.
            obj[p] = obj[p];
        }
        return x;
    }();

    // 'p' still has value of 'clean'.
}
// Bad
function bar() {
    var p = 'clean';
    function() {
        var obj = { dirty: 'dirty' };
        for (p in obj) { // Oh no, missing 'var' here!
            obj[p] = obj[p];
        }
        return x;
    }();

    // 'p' is trashed and has value of 'dirty'!
}

Use this rule by referencing it:

<rule ref="category/ecmascript/bestpractices.xml/ScopeForInVariable" />

UseBaseWithParseInt

Since: PMD 5.0.1

Priority: High (1)

This rule checks for usages of parseInt. While the second parameter is optional and usually defaults to 10 (base/radix is 10 for a decimal number), different implementations may behave differently. It also improves readability, if the base is given.