2 * @fileoverview Rule to replace assignment expressions with operator assignment
3 * @author Brandon Mills
7 //------------------------------------------------------------------------------
9 //------------------------------------------------------------------------------
11 const astUtils = require("./utils/ast-utils");
13 //------------------------------------------------------------------------------
15 //------------------------------------------------------------------------------
18 * Checks whether an operator is commutative and has an operator assignment
20 * @param {string} operator Operator to check.
21 * @returns {boolean} True if the operator is commutative and has a
24 function isCommutativeOperatorWithShorthand(operator) {
25 return ["*", "&", "^", "|"].indexOf(operator) >= 0;
29 * Checks whether an operator is not commutative and has an operator assignment
31 * @param {string} operator Operator to check.
32 * @returns {boolean} True if the operator is not commutative and has
35 function isNonCommutativeOperatorWithShorthand(operator) {
36 return ["+", "-", "/", "%", "<<", ">>", ">>>", "**"].indexOf(operator) >= 0;
39 //------------------------------------------------------------------------------
41 //------------------------------------------------------------------------------
44 * Determines if the left side of a node can be safely fixed (i.e. if it activates the same getters/setters and)
45 * toString calls regardless of whether assignment shorthand is used)
46 * @param {ASTNode} node The node on the left side of the expression
47 * @returns {boolean} `true` if the node can be fixed
49 function canBeFixed(node) {
51 node.type === "Identifier" ||
53 node.type === "MemberExpression" &&
54 (node.object.type === "Identifier" || node.object.type === "ThisExpression") &&
55 (!node.computed || node.property.type === "Literal")
65 description: "require or disallow assignment operator shorthand where possible",
66 category: "Stylistic Issues",
68 url: "https://eslint.org/docs/rules/operator-assignment"
73 enum: ["always", "never"]
79 replaced: "Assignment (=) can be replaced with operator assignment ({{operator}}=).",
80 unexpected: "Unexpected operator assignment ({{operator}}=) shorthand."
86 const sourceCode = context.getSourceCode();
89 * Returns the operator token of an AssignmentExpression or BinaryExpression
90 * @param {ASTNode} node An AssignmentExpression or BinaryExpression node
91 * @returns {Token} The operator token in the node
93 function getOperatorToken(node) {
94 return sourceCode.getFirstTokenBetween(node.left, node.right, token => token.value === node.operator);
98 * Ensures that an assignment uses the shorthand form where possible.
99 * @param {ASTNode} node An AssignmentExpression node.
102 function verify(node) {
103 if (node.operator !== "=" || node.right.type !== "BinaryExpression") {
107 const left = node.left;
108 const expr = node.right;
109 const operator = expr.operator;
111 if (isCommutativeOperatorWithShorthand(operator) || isNonCommutativeOperatorWithShorthand(operator)) {
112 if (astUtils.isSameReference(left, expr.left, true)) {
115 messageId: "replaced",
118 if (canBeFixed(left) && canBeFixed(expr.left)) {
119 const equalsToken = getOperatorToken(node);
120 const operatorToken = getOperatorToken(expr);
121 const leftText = sourceCode.getText().slice(node.range[0], equalsToken.range[0]);
122 const rightText = sourceCode.getText().slice(operatorToken.range[1], node.right.range[1]);
124 // Check for comments that would be removed.
125 if (sourceCode.commentsExistBetween(equalsToken, operatorToken)) {
129 return fixer.replaceText(node, `${leftText}${expr.operator}=${rightText}`);
134 } else if (astUtils.isSameReference(left, expr.right, true) && isCommutativeOperatorWithShorthand(operator)) {
137 * This case can't be fixed safely.
138 * If `a` and `b` both have custom valueOf() behavior, then fixing `a = b * a` to `a *= b` would
139 * change the execution order of the valueOf() functions.
143 messageId: "replaced",
151 * Warns if an assignment expression uses operator assignment shorthand.
152 * @param {ASTNode} node An AssignmentExpression node.
155 function prohibit(node) {
156 if (node.operator !== "=" && !astUtils.isLogicalAssignmentOperator(node.operator)) {
159 messageId: "unexpected",
160 data: { operator: node.operator },
162 if (canBeFixed(node.left)) {
163 const firstToken = sourceCode.getFirstToken(node);
164 const operatorToken = getOperatorToken(node);
165 const leftText = sourceCode.getText().slice(node.range[0], operatorToken.range[0]);
166 const newOperator = node.operator.slice(0, -1);
169 // Check for comments that would be duplicated.
170 if (sourceCode.commentsExistBetween(firstToken, operatorToken)) {
174 // If this change would modify precedence (e.g. `foo *= bar + 1` => `foo = foo * (bar + 1)`), parenthesize the right side.
176 astUtils.getPrecedence(node.right) <= astUtils.getPrecedence({ type: "BinaryExpression", operator: newOperator }) &&
177 !astUtils.isParenthesised(sourceCode, node.right)
179 rightText = `${sourceCode.text.slice(operatorToken.range[1], node.right.range[0])}(${sourceCode.getText(node.right)})`;
181 const tokenAfterOperator = sourceCode.getTokenAfter(operatorToken, { includeComments: true });
182 let rightTextPrefix = "";
185 operatorToken.range[1] === tokenAfterOperator.range[0] &&
186 !astUtils.canTokensBeAdjacent({ type: "Punctuator", value: newOperator }, tokenAfterOperator)
188 rightTextPrefix = " "; // foo+=+bar -> foo= foo+ +bar
191 rightText = `${rightTextPrefix}${sourceCode.text.slice(operatorToken.range[1], node.range[1])}`;
194 return fixer.replaceText(node, `${leftText}= ${leftText}${newOperator}${rightText}`);
203 AssignmentExpression: context.options[0] !== "never" ? verify : prohibit