--- /dev/null
+/**
+ * @fileoverview A rule to control the style of variable initializations.
+ * @author Colin Ihrig
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Checks whether or not a given node is a for loop.
+ * @param {ASTNode} block A node to check.
+ * @returns {boolean} `true` when the node is a for loop.
+ */
+function isForLoop(block) {
+ return block.type === "ForInStatement" ||
+ block.type === "ForOfStatement" ||
+ block.type === "ForStatement";
+}
+
+/**
+ * Checks whether or not a given declarator node has its initializer.
+ * @param {ASTNode} node A declarator node to check.
+ * @returns {boolean} `true` when the node has its initializer.
+ */
+function isInitialized(node) {
+ const declaration = node.parent;
+ const block = declaration.parent;
+
+ if (isForLoop(block)) {
+ if (block.type === "ForStatement") {
+ return block.init === declaration;
+ }
+ return block.left === declaration;
+ }
+ return Boolean(node.init);
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "require or disallow initialization in variable declarations",
+ category: "Variables",
+ recommended: false,
+ url: "https://eslint.org/docs/rules/init-declarations"
+ },
+
+ schema: {
+ anyOf: [
+ {
+ type: "array",
+ items: [
+ {
+ enum: ["always"]
+ }
+ ],
+ minItems: 0,
+ maxItems: 1
+ },
+ {
+ type: "array",
+ items: [
+ {
+ enum: ["never"]
+ },
+ {
+ type: "object",
+ properties: {
+ ignoreForLoopInit: {
+ type: "boolean"
+ }
+ },
+ additionalProperties: false
+ }
+ ],
+ minItems: 0,
+ maxItems: 2
+ }
+ ]
+ },
+ messages: {
+ initialized: "Variable '{{idName}}' should be initialized on declaration.",
+ notInitialized: "Variable '{{idName}}' should not be initialized on declaration."
+ }
+ },
+
+ create(context) {
+
+ const MODE_ALWAYS = "always",
+ MODE_NEVER = "never";
+
+ const mode = context.options[0] || MODE_ALWAYS;
+ const params = context.options[1] || {};
+
+ //--------------------------------------------------------------------------
+ // Public API
+ //--------------------------------------------------------------------------
+
+ return {
+ "VariableDeclaration:exit"(node) {
+
+ const kind = node.kind,
+ declarations = node.declarations;
+
+ for (let i = 0; i < declarations.length; ++i) {
+ const declaration = declarations[i],
+ id = declaration.id,
+ initialized = isInitialized(declaration),
+ isIgnoredForLoop = params.ignoreForLoopInit && isForLoop(node.parent);
+ let messageId = "";
+
+ if (mode === MODE_ALWAYS && !initialized) {
+ messageId = "initialized";
+ } else if (mode === MODE_NEVER && kind !== "const" && initialized && !isIgnoredForLoop) {
+ messageId = "notInitialized";
+ }
+
+ if (id.type === "Identifier" && messageId) {
+ context.report({
+ node: declaration,
+ messageId,
+ data: {
+ idName: id.name
+ }
+ });
+ }
+ }
+ }
+ };
+ }
+};