2 * @fileoverview Rule to disallow Math.pow in favor of the ** operator
3 * @author Milos Djermanovic
8 //------------------------------------------------------------------------------
10 //------------------------------------------------------------------------------
12 const astUtils
= require("./utils/ast-utils");
13 const { CALL
, ReferenceTracker
} = require("eslint-utils");
15 //------------------------------------------------------------------------------
17 //------------------------------------------------------------------------------
19 const PRECEDENCE_OF_EXPONENTIATION_EXPR
= astUtils
.getPrecedence({ type
: "BinaryExpression", operator
: "**" });
22 * Determines whether the given node needs parens if used as the base in an exponentiation binary expression.
23 * @param {ASTNode} base The node to check.
24 * @returns {boolean} `true` if the node needs to be parenthesised.
26 function doesBaseNeedParens(base
) {
29 // '**' is right-associative, parens are needed when Math.pow(a ** b, c) is converted to (a ** b) ** c
30 astUtils
.getPrecedence(base
) <= PRECEDENCE_OF_EXPONENTIATION_EXPR
||
32 // An unary operator cannot be used immediately before an exponentiation expression
33 base
.type
=== "AwaitExpression" ||
34 base
.type
=== "UnaryExpression"
39 * Determines whether the given node needs parens if used as the exponent in an exponentiation binary expression.
40 * @param {ASTNode} exponent The node to check.
41 * @returns {boolean} `true` if the node needs to be parenthesised.
43 function doesExponentNeedParens(exponent
) {
45 // '**' is right-associative, there is no need for parens when Math.pow(a, b ** c) is converted to a ** b ** c
46 return astUtils
.getPrecedence(exponent
) < PRECEDENCE_OF_EXPONENTIATION_EXPR
;
50 * Determines whether an exponentiation binary expression at the place of the given node would need parens.
51 * @param {ASTNode} node A node that would be replaced by an exponentiation binary expression.
52 * @param {SourceCode} sourceCode A SourceCode object.
53 * @returns {boolean} `true` if the expression needs to be parenthesised.
55 function doesExponentiationExpressionNeedParens(node
, sourceCode
) {
56 const parent
= node
.parent
.type
=== "ChainExpression" ? node
.parent
.parent
: node
.parent
;
59 parent
.type
=== "ClassDeclaration" ||
61 parent
.type
.endsWith("Expression") &&
62 astUtils
.getPrecedence(parent
) >= PRECEDENCE_OF_EXPONENTIATION_EXPR
&&
63 !(parent
.type
=== "BinaryExpression" && parent
.operator
=== "**" && parent
.right
=== node
) &&
64 !((parent
.type
=== "CallExpression" || parent
.type
=== "NewExpression") && parent
.arguments
.includes(node
)) &&
65 !(parent
.type
=== "MemberExpression" && parent
.computed
&& parent
.property
=== node
) &&
66 !(parent
.type
=== "ArrayExpression")
70 return needsParens
&& !astUtils
.isParenthesised(sourceCode
, node
);
74 * Optionally parenthesizes given text.
75 * @param {string} text The text to parenthesize.
76 * @param {boolean} shouldParenthesize If `true`, the text will be parenthesised.
77 * @returns {string} parenthesised or unchanged text.
79 function parenthesizeIfShould(text
, shouldParenthesize
) {
80 return shouldParenthesize
? `(${text})` : text
;
83 //------------------------------------------------------------------------------
85 //------------------------------------------------------------------------------
92 description
: "disallow the use of `Math.pow` in favor of the `**` operator",
93 category
: "Stylistic Issues",
95 url
: "https://eslint.org/docs/rules/prefer-exponentiation-operator"
102 useExponentiation
: "Use the '**' operator instead of 'Math.pow'."
107 const sourceCode
= context
.getSourceCode();
110 * Reports the given node.
111 * @param {ASTNode} node 'Math.pow()' node to report.
114 function report(node
) {
117 messageId
: "useExponentiation",
120 node
.arguments
.length
!== 2 ||
121 node
.arguments
.some(arg
=> arg
.type
=== "SpreadElement") ||
122 sourceCode
.getCommentsInside(node
).length
> 0
127 const base
= node
.arguments
[0],
128 exponent
= node
.arguments
[1],
129 baseText
= sourceCode
.getText(base
),
130 exponentText
= sourceCode
.getText(exponent
),
131 shouldParenthesizeBase
= doesBaseNeedParens(base
),
132 shouldParenthesizeExponent
= doesExponentNeedParens(exponent
),
133 shouldParenthesizeAll
= doesExponentiationExpressionNeedParens(node
, sourceCode
);
138 if (!shouldParenthesizeAll
) {
139 if (!shouldParenthesizeBase
) {
140 const firstReplacementToken
= sourceCode
.getFirstToken(base
),
141 tokenBefore
= sourceCode
.getTokenBefore(node
);
145 tokenBefore
.range
[1] === node
.range
[0] &&
146 !astUtils
.canTokensBeAdjacent(tokenBefore
, firstReplacementToken
)
148 prefix
= " "; // a+Math.pow(++b, c) -> a+ ++b**c
151 if (!shouldParenthesizeExponent
) {
152 const lastReplacementToken
= sourceCode
.getLastToken(exponent
),
153 tokenAfter
= sourceCode
.getTokenAfter(node
);
157 node
.range
[1] === tokenAfter
.range
[0] &&
158 !astUtils
.canTokensBeAdjacent(lastReplacementToken
, tokenAfter
)
160 suffix
= " "; // Math.pow(a, b)in c -> a**b in c
165 const baseReplacement
= parenthesizeIfShould(baseText
, shouldParenthesizeBase
),
166 exponentReplacement
= parenthesizeIfShould(exponentText
, shouldParenthesizeExponent
),
167 replacement
= parenthesizeIfShould(`${baseReplacement}**${exponentReplacement}`, shouldParenthesizeAll
);
169 return fixer
.replaceText(node
, `${prefix}${replacement}${suffix}`);
176 const scope
= context
.getScope();
177 const tracker
= new ReferenceTracker(scope
);
180 pow
: { [CALL
]: true }
184 for (const { node
} of tracker
.iterateGlobalReferences(trackMap
)) {