no-unneeded-ternary.js
6.79 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
/**
* @fileoverview Rule to flag no-unneeded-ternary
* @author Gyandeep Singh
*/
"use strict";
const astUtils = require("./utils/ast-utils");
// Operators that always result in a boolean value
const BOOLEAN_OPERATORS = new Set(["==", "===", "!=", "!==", ">", ">=", "<", "<=", "in", "instanceof"]);
const OPERATOR_INVERSES = {
"==": "!=",
"!=": "==",
"===": "!==",
"!==": "==="
// Operators like < and >= are not true inverses, since both will return false with NaN.
};
const OR_PRECEDENCE = astUtils.getPrecedence({ type: "LogicalExpression", operator: "||" });
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "Disallow ternary operators when simpler alternatives exist",
recommended: false,
url: "https://eslint.org/docs/rules/no-unneeded-ternary"
},
schema: [
{
type: "object",
properties: {
defaultAssignment: {
type: "boolean",
default: true
}
},
additionalProperties: false
}
],
fixable: "code",
messages: {
unnecessaryConditionalExpression: "Unnecessary use of boolean literals in conditional expression.",
unnecessaryConditionalAssignment: "Unnecessary use of conditional expression for default assignment."
}
},
create(context) {
const options = context.options[0] || {};
const defaultAssignment = options.defaultAssignment !== false;
const sourceCode = context.getSourceCode();
/**
* Test if the node is a boolean literal
* @param {ASTNode} node The node to report.
* @returns {boolean} True if the its a boolean literal
* @private
*/
function isBooleanLiteral(node) {
return node.type === "Literal" && typeof node.value === "boolean";
}
/**
* Creates an expression that represents the boolean inverse of the expression represented by the original node
* @param {ASTNode} node A node representing an expression
* @returns {string} A string representing an inverted expression
*/
function invertExpression(node) {
if (node.type === "BinaryExpression" && Object.prototype.hasOwnProperty.call(OPERATOR_INVERSES, node.operator)) {
const operatorToken = sourceCode.getFirstTokenBetween(
node.left,
node.right,
token => token.value === node.operator
);
const text = sourceCode.getText();
return text.slice(node.range[0],
operatorToken.range[0]) + OPERATOR_INVERSES[node.operator] + text.slice(operatorToken.range[1], node.range[1]);
}
if (astUtils.getPrecedence(node) < astUtils.getPrecedence({ type: "UnaryExpression" })) {
return `!(${astUtils.getParenthesisedText(sourceCode, node)})`;
}
return `!${astUtils.getParenthesisedText(sourceCode, node)}`;
}
/**
* Tests if a given node always evaluates to a boolean value
* @param {ASTNode} node An expression node
* @returns {boolean} True if it is determined that the node will always evaluate to a boolean value
*/
function isBooleanExpression(node) {
return node.type === "BinaryExpression" && BOOLEAN_OPERATORS.has(node.operator) ||
node.type === "UnaryExpression" && node.operator === "!";
}
/**
* Test if the node matches the pattern id ? id : expression
* @param {ASTNode} node The ConditionalExpression to check.
* @returns {boolean} True if the pattern is matched, and false otherwise
* @private
*/
function matchesDefaultAssignment(node) {
return node.test.type === "Identifier" &&
node.consequent.type === "Identifier" &&
node.test.name === node.consequent.name;
}
return {
ConditionalExpression(node) {
if (isBooleanLiteral(node.alternate) && isBooleanLiteral(node.consequent)) {
context.report({
node,
messageId: "unnecessaryConditionalExpression",
fix(fixer) {
if (node.consequent.value === node.alternate.value) {
// Replace `foo ? true : true` with just `true`, but don't replace `foo() ? true : true`
return node.test.type === "Identifier" ? fixer.replaceText(node, node.consequent.value.toString()) : null;
}
if (node.alternate.value) {
// Replace `foo() ? false : true` with `!(foo())`
return fixer.replaceText(node, invertExpression(node.test));
}
// Replace `foo ? true : false` with `foo` if `foo` is guaranteed to be a boolean, or `!!foo` otherwise.
return fixer.replaceText(node, isBooleanExpression(node.test) ? astUtils.getParenthesisedText(sourceCode, node.test) : `!${invertExpression(node.test)}`);
}
});
} else if (!defaultAssignment && matchesDefaultAssignment(node)) {
context.report({
node,
messageId: "unnecessaryConditionalAssignment",
fix: fixer => {
const shouldParenthesizeAlternate =
(
astUtils.getPrecedence(node.alternate) < OR_PRECEDENCE ||
astUtils.isCoalesceExpression(node.alternate)
) &&
!astUtils.isParenthesised(sourceCode, node.alternate);
const alternateText = shouldParenthesizeAlternate
? `(${sourceCode.getText(node.alternate)})`
: astUtils.getParenthesisedText(sourceCode, node.alternate);
const testText = astUtils.getParenthesisedText(sourceCode, node.test);
return fixer.replaceText(node, `${testText} || ${alternateText}`);
}
});
}
}
};
}
};