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/**
* @fileoverview Rule to disallow Math.pow in favor of the ** operator
* @author Milos Djermanovic
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
const { CALL, ReferenceTracker } = require("eslint-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const PRECEDENCE_OF_EXPONENTIATION_EXPR = astUtils.getPrecedence({ type: "BinaryExpression", operator: "**" });
/**
* Determines whether the given node needs parens if used as the base in an exponentiation binary expression.
* @param {ASTNode} base The node to check.
* @returns {boolean} `true` if the node needs to be parenthesised.
*/
function doesBaseNeedParens(base) {
return (
// '**' is right-associative, parens are needed when Math.pow(a ** b, c) is converted to (a ** b) ** c
astUtils.getPrecedence(base) <= PRECEDENCE_OF_EXPONENTIATION_EXPR ||
// An unary operator cannot be used immediately before an exponentiation expression
base.type === "UnaryExpression"
);
}
/**
* Determines whether the given node needs parens if used as the exponent in an exponentiation binary expression.
* @param {ASTNode} exponent The node to check.
* @returns {boolean} `true` if the node needs to be parenthesised.
*/
function doesExponentNeedParens(exponent) {
// '**' is right-associative, there is no need for parens when Math.pow(a, b ** c) is converted to a ** b ** c
return astUtils.getPrecedence(exponent) < PRECEDENCE_OF_EXPONENTIATION_EXPR;
}
/**
* Determines whether an exponentiation binary expression at the place of the given node would need parens.
* @param {ASTNode} node A node that would be replaced by an exponentiation binary expression.
* @param {SourceCode} sourceCode A SourceCode object.
* @returns {boolean} `true` if the expression needs to be parenthesised.
*/
function doesExponentiationExpressionNeedParens(node, sourceCode) {
const parent = node.parent.type === "ChainExpression" ? node.parent.parent : node.parent;
const needsParens = (
parent.type === "ClassDeclaration" ||
(
parent.type.endsWith("Expression") &&
astUtils.getPrecedence(parent) >= PRECEDENCE_OF_EXPONENTIATION_EXPR &&
!(parent.type === "BinaryExpression" && parent.operator === "**" && parent.right === node) &&
!((parent.type === "CallExpression" || parent.type === "NewExpression") && parent.arguments.includes(node)) &&
!(parent.type === "MemberExpression" && parent.computed && parent.property === node) &&
!(parent.type === "ArrayExpression")
)
);
return needsParens && !astUtils.isParenthesised(sourceCode, node);
}
/**
* Optionally parenthesizes given text.
* @param {string} text The text to parenthesize.
* @param {boolean} shouldParenthesize If `true`, the text will be parenthesised.
* @returns {string} parenthesised or unchanged text.
*/
function parenthesizeIfShould(text, shouldParenthesize) {
return shouldParenthesize ? `(${text})` : text;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "disallow the use of `Math.pow` in favor of the `**` operator",
category: "Stylistic Issues",
recommended: false,
url: "https://eslint.org/docs/rules/prefer-exponentiation-operator"
},
schema: [],
fixable: "code",
messages: {
useExponentiation: "Use the '**' operator instead of 'Math.pow'."
}
},
create(context) {
const sourceCode = context.getSourceCode();
/**
* Reports the given node.
* @param {ASTNode} node 'Math.pow()' node to report.
* @returns {void}
*/
function report(node) {
context.report({
node,
messageId: "useExponentiation",
fix(fixer) {
if (
node.arguments.length !== 2 ||
node.arguments.some(arg => arg.type === "SpreadElement") ||
sourceCode.getCommentsInside(node).length > 0
) {
return null;
}
const base = node.arguments[0],
exponent = node.arguments[1],
baseText = sourceCode.getText(base),
exponentText = sourceCode.getText(exponent),
shouldParenthesizeBase = doesBaseNeedParens(base),
shouldParenthesizeExponent = doesExponentNeedParens(exponent),
shouldParenthesizeAll = doesExponentiationExpressionNeedParens(node, sourceCode);
let prefix = "",
suffix = "";
if (!shouldParenthesizeAll) {
if (!shouldParenthesizeBase) {
const firstReplacementToken = sourceCode.getFirstToken(base),
tokenBefore = sourceCode.getTokenBefore(node);
if (
tokenBefore &&
tokenBefore.range[1] === node.range[0] &&
!astUtils.canTokensBeAdjacent(tokenBefore, firstReplacementToken)
) {
prefix = " "; // a+Math.pow(++b, c) -> a+ ++b**c
}
}
if (!shouldParenthesizeExponent) {
const lastReplacementToken = sourceCode.getLastToken(exponent),
tokenAfter = sourceCode.getTokenAfter(node);
if (
tokenAfter &&
node.range[1] === tokenAfter.range[0] &&
!astUtils.canTokensBeAdjacent(lastReplacementToken, tokenAfter)
) {
suffix = " "; // Math.pow(a, b)in c -> a**b in c
}
}
}
const baseReplacement = parenthesizeIfShould(baseText, shouldParenthesizeBase),
exponentReplacement = parenthesizeIfShould(exponentText, shouldParenthesizeExponent),
replacement = parenthesizeIfShould(`${baseReplacement}**${exponentReplacement}`, shouldParenthesizeAll);
return fixer.replaceText(node, `${prefix}${replacement}${suffix}`);
}
});
}
return {
Program() {
const scope = context.getScope();
const tracker = new ReferenceTracker(scope);
const trackMap = {
Math: {
pow: { [CALL]: true }
}
};
for (const { node } of tracker.iterateGlobalReferences(trackMap)) {
report(node);
}
}
};
}
};
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