Best Practices | PMD Source Code Analyzer

Rules which enforce generally accepted best practices.

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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;
}

This rule has the following properties:

Name	Default Value	Description	Multivalued
rhinoLanguageVersion	VERSION_DEFAULT	Specifies the Rhino Language Version to use for parsing. Defaults to Rhino default.	no
recordingLocalJsDocComments	true	Specifies that JsDoc comments are produced in the AST.	no
recordingComments	true	Specifies that comments are produced in the AST.	no

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.