Current File : //var/www/html/node_modules/eslint/lib/rules/no-loss-of-precision.js
/**
* @fileoverview Rule to flag numbers that will lose significant figure precision at runtime
* @author Jacob Moore
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow literal numbers that lose precision",
recommended: true,
url: "https://eslint.org/docs/rules/no-loss-of-precision"
},
schema: [],
messages: {
noLossOfPrecision: "This number literal will lose precision at runtime."
}
},
create(context) {
/**
* Returns whether the node is number literal
* @param {Node} node the node literal being evaluated
* @returns {boolean} true if the node is a number literal
*/
function isNumber(node) {
return typeof node.value === "number";
}
/**
* Gets the source code of the given number literal. Removes `_` numeric separators from the result.
* @param {Node} node the number `Literal` node
* @returns {string} raw source code of the literal, without numeric separators
*/
function getRaw(node) {
return node.raw.replace(/_/gu, "");
}
/**
* Checks whether the number is base ten
* @param {ASTNode} node the node being evaluated
* @returns {boolean} true if the node is in base ten
*/
function isBaseTen(node) {
const prefixes = ["0x", "0X", "0b", "0B", "0o", "0O"];
return prefixes.every(prefix => !node.raw.startsWith(prefix)) &&
!/^0[0-7]+$/u.test(node.raw);
}
/**
* Checks that the user-intended non-base ten number equals the actual number after is has been converted to the Number type
* @param {Node} node the node being evaluated
* @returns {boolean} true if they do not match
*/
function notBaseTenLosesPrecision(node) {
const rawString = getRaw(node).toUpperCase();
let base = 0;
if (rawString.startsWith("0B")) {
base = 2;
} else if (rawString.startsWith("0X")) {
base = 16;
} else {
base = 8;
}
return !rawString.endsWith(node.value.toString(base).toUpperCase());
}
/**
* Adds a decimal point to the numeric string at index 1
* @param {string} stringNumber the numeric string without any decimal point
* @returns {string} the numeric string with a decimal point in the proper place
*/
function addDecimalPointToNumber(stringNumber) {
return `${stringNumber.slice(0, 1)}.${stringNumber.slice(1)}`;
}
/**
* Returns the number stripped of leading zeros
* @param {string} numberAsString the string representation of the number
* @returns {string} the stripped string
*/
function removeLeadingZeros(numberAsString) {
return numberAsString.replace(/^0*/u, "");
}
/**
* Returns the number stripped of trailing zeros
* @param {string} numberAsString the string representation of the number
* @returns {string} the stripped string
*/
function removeTrailingZeros(numberAsString) {
return numberAsString.replace(/0*$/u, "");
}
/**
* Converts an integer to to an object containing the integer's coefficient and order of magnitude
* @param {string} stringInteger the string representation of the integer being converted
* @returns {Object} the object containing the integer's coefficient and order of magnitude
*/
function normalizeInteger(stringInteger) {
const significantDigits = removeTrailingZeros(removeLeadingZeros(stringInteger));
return {
magnitude: stringInteger.startsWith("0") ? stringInteger.length - 2 : stringInteger.length - 1,
coefficient: addDecimalPointToNumber(significantDigits)
};
}
/**
*
* Converts a float to to an object containing the floats's coefficient and order of magnitude
* @param {string} stringFloat the string representation of the float being converted
* @returns {Object} the object containing the integer's coefficient and order of magnitude
*/
function normalizeFloat(stringFloat) {
const trimmedFloat = removeLeadingZeros(stringFloat);
if (trimmedFloat.startsWith(".")) {
const decimalDigits = trimmedFloat.split(".").pop();
const significantDigits = removeLeadingZeros(decimalDigits);
return {
magnitude: significantDigits.length - decimalDigits.length - 1,
coefficient: addDecimalPointToNumber(significantDigits)
};
}
return {
magnitude: trimmedFloat.indexOf(".") - 1,
coefficient: addDecimalPointToNumber(trimmedFloat.replace(".", ""))
};
}
/**
* Converts a base ten number to proper scientific notation
* @param {string} stringNumber the string representation of the base ten number to be converted
* @returns {string} the number converted to scientific notation
*/
function convertNumberToScientificNotation(stringNumber) {
const splitNumber = stringNumber.replace("E", "e").split("e");
const originalCoefficient = splitNumber[0];
const normalizedNumber = stringNumber.includes(".") ? normalizeFloat(originalCoefficient)
: normalizeInteger(originalCoefficient);
const normalizedCoefficient = normalizedNumber.coefficient;
const magnitude = splitNumber.length > 1 ? (parseInt(splitNumber[1], 10) + normalizedNumber.magnitude)
: normalizedNumber.magnitude;
return `${normalizedCoefficient}e${magnitude}`;
}
/**
* Checks that the user-intended base ten number equals the actual number after is has been converted to the Number type
* @param {Node} node the node being evaluated
* @returns {boolean} true if they do not match
*/
function baseTenLosesPrecision(node) {
const normalizedRawNumber = convertNumberToScientificNotation(getRaw(node));
const requestedPrecision = normalizedRawNumber.split("e")[0].replace(".", "").length;
if (requestedPrecision > 100) {
return true;
}
const storedNumber = node.value.toPrecision(requestedPrecision);
const normalizedStoredNumber = convertNumberToScientificNotation(storedNumber);
return normalizedRawNumber !== normalizedStoredNumber;
}
/**
* Checks that the user-intended number equals the actual number after is has been converted to the Number type
* @param {Node} node the node being evaluated
* @returns {boolean} true if they do not match
*/
function losesPrecision(node) {
return isBaseTen(node) ? baseTenLosesPrecision(node) : notBaseTenLosesPrecision(node);
}
return {
Literal(node) {
if (node.value && isNumber(node) && losesPrecision(node)) {
context.report({
messageId: "noLossOfPrecision",
node
});
}
}
};
}
};
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