vars-on-top.js
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/**
* @fileoverview Rule to enforce var declarations are only at the top of a function.
* @author Danny Fritz
* @author Gyandeep Singh
* @copyright 2014 Danny Fritz. All rights reserved.
* @copyright 2014 Gyandeep Singh. All rights reserved.
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = function(context) {
var errorMessage = "All \"var\" declarations must be at the top of the function scope.";
//--------------------------------------------------------------------------
// Helpers
//--------------------------------------------------------------------------
/**
* @param {ASTNode} node - any node
* @returns {Boolean} whether the given node structurally represents a directive
*/
function looksLikeDirective(node) {
return node.type === "ExpressionStatement" &&
node.expression.type === "Literal" && typeof node.expression.value === "string";
}
/**
* Check to see if its a ES6 import declaration
* @param {ASTNode} node - any node
* @returns {Boolean} whether the given node represents a import declaration
*/
function looksLikeImport(node) {
return node.type === "ImportDeclaration" || node.type === "ImportSpecifier" ||
node.type === "ImportDefaultSpecifier" || node.type === "ImportNamespaceSpecifier";
}
/**
* Checks whether this variable is on top of the block body
* @param {ASTNode} node - The node to check
* @param {ASTNode[]} statements - collection of ASTNodes for the parent node block
* @returns {Boolean} True if var is on top otherwise false
*/
function isVarOnTop(node, statements) {
var i = 0, l = statements.length;
// skip over directives
for (; i < l; ++i) {
if (!looksLikeDirective(statements[i]) && !looksLikeImport(statements[i])) {
break;
}
}
for (; i < l; ++i) {
if (statements[i].type !== "VariableDeclaration") {
return false;
}
if (statements[i] === node) {
return true;
}
}
}
/**
* Checks whether variable is on top at the global level
* @param {ASTNode} node - The node to check
* @param {ASTNode} parent - Parent of the node
* @returns {void}
*/
function globalVarCheck(node, parent) {
if (!isVarOnTop(node, parent.body)) {
context.report(node, errorMessage);
}
}
/**
* Checks whether variable is on top at functional block scope level
* @param {ASTNode} node - The node to check
* @param {ASTNode} parent - Parent of the node
* @param {ASTNode} grandParent - Parent of the node's parent
* @returns {void}
*/
function blockScopeVarCheck(node, parent, grandParent) {
if (!(/Function/.test(grandParent.type) &&
parent.type === "BlockStatement" &&
isVarOnTop(node, parent.body))) {
context.report(node, errorMessage);
}
}
//--------------------------------------------------------------------------
// Public API
//--------------------------------------------------------------------------
return {
"VariableDeclaration": function(node) {
var ancestors = context.getAncestors();
var parent = ancestors.pop();
var grandParent = ancestors.pop();
if (node.kind === "var") { // check variable is `var` type and not `let` or `const`
if (parent.type === "Program") { // That means its a global variable
globalVarCheck(node, parent);
} else {
blockScopeVarCheck(node, parent, grandParent);
}
}
}
};
};
module.exports.schema = [];