/
prefer-string-slice.js
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/
prefer-string-slice.js
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'use strict';
const eslintTemplateVisitor = require('eslint-template-visitor');
const getDocumentationUrl = require('./utils/get-documentation-url');
const templates = eslintTemplateVisitor();
const objectVariable = templates.variable();
const argumentsVariable = templates.spreadVariable();
const substrCallTemplate = templates.template`${objectVariable}.substr(${argumentsVariable})`;
const substringCallTemplate = templates.template`${objectVariable}.substring(${argumentsVariable})`;
const isLiteralNumber = node => node && node.type === 'Literal' && typeof node.value === 'number';
const getNumericValue = node => {
if (isLiteralNumber(node)) {
return node.value;
}
if (node.type === 'UnaryExpression' && node.operator === '-') {
return -getNumericValue(node.argument);
}
};
// This handles cases where the argument is very likely to be a number, such as `.substring('foo'.length)`.
const isLengthProperty = node => (
node &&
node.type === 'MemberExpression' &&
node.computed === false &&
node.property.type === 'Identifier' &&
node.property.name === 'length'
);
const isLikelyNumeric = node => isLiteralNumber(node) || isLengthProperty(node);
const create = context => {
const sourceCode = context.getSourceCode();
const getNodeText = node => {
const text = sourceCode.getText(node);
const before = sourceCode.getTokenBefore(node);
const after = sourceCode.getTokenAfter(node);
if (
(before && before.type === 'Punctuator' && before.value === '(') &&
(after && after.type === 'Punctuator' && after.value === ')')
) {
return `(${text})`;
}
return text;
};
return templates.visitor({
[substrCallTemplate](node) {
const objectNode = substrCallTemplate.context.getMatch(objectVariable);
const argumentNodes = substrCallTemplate.context.getMatch(argumentsVariable);
const problem = {
node,
message: 'Prefer `String#slice()` over `String#substr()`.'
};
const firstArgument = argumentNodes[0] ? sourceCode.getText(argumentNodes[0]) : undefined;
const secondArgument = argumentNodes[1] ? sourceCode.getText(argumentNodes[1]) : undefined;
let sliceArguments;
if (argumentNodes.length === 0) {
sliceArguments = [];
} else if (argumentNodes.length === 1) {
sliceArguments = [firstArgument];
} else if (argumentNodes.length === 2) {
if (firstArgument === '0') {
sliceArguments = [firstArgument];
if (isLiteralNumber(secondArgument) || isLengthProperty(argumentNodes[1])) {
sliceArguments.push(secondArgument)
} else if (getNumericValue(argumentNodes[1]) !== undefined) {
sliceArguments.push(Math.max(0, getNumericValue(argumentNodes[1])))
} else {
sliceArguments.push(`Math.max(0, ${secondArgument})`)
}
} else if (
isLiteralNumber(argumentNodes[0]) &&
isLiteralNumber(argumentNodes[1])
) {
sliceArguments = [
firstArgument,
argumentNodes[0].value + argumentNodes[1].value
];
} else if (
isLikelyNumeric(argumentNodes[0]) &&
isLikelyNumeric(argumentNodes[1])
) {
sliceArguments = [firstArgument, firstArgument + ' + ' + secondArgument];
}
}
if (sliceArguments) {
const objectText = getNodeText(objectNode);
problem.fix = fixer => fixer.replaceText(node, `${objectText}.slice(${sliceArguments.join(', ')})`);
}
context.report(problem);
},
[substringCallTemplate](node) {
const objectNode = substringCallTemplate.context.getMatch(objectVariable);
const argumentNodes = substringCallTemplate.context.getMatch(argumentsVariable);
const problem = {
node,
message: 'Prefer `String#slice()` over `String#substring()`.'
};
const firstArgument = argumentNodes[0] ? sourceCode.getText(argumentNodes[0]) : undefined;
const secondArgument = argumentNodes[1] ? sourceCode.getText(argumentNodes[1]) : undefined;
const firstNumber = argumentNodes[0] ? getNumericValue(argumentNodes[0]) : undefined;
let sliceArguments;
if (argumentNodes.length === 0) {
sliceArguments = [];
} else if (argumentNodes.length === 1) {
if (firstNumber !== undefined) {
sliceArguments = [Math.max(0, firstNumber)];
} else if (isLengthProperty(argumentNodes[0])) {
sliceArguments = [firstArgument];
} else {
sliceArguments = [`Math.max(0, ${firstArgument})`];
}
} else if (argumentNodes.length === 2) {
const secondNumber = getNumericValue(argumentNodes[1]);
if (firstNumber !== undefined && secondNumber !== undefined) {
sliceArguments = firstNumber > secondNumber ?
[Math.max(0, secondNumber), Math.max(0, firstNumber)] :
[Math.max(0, firstNumber), Math.max(0, secondNumber)];
} else if (firstNumber === 0 || secondNumber === 0) {
sliceArguments = [0, `Math.max(0, ${firstNumber === 0 ? secondArgument : firstArgument})`];
} else {
// As values aren't Literal, we can not know whether secondArgument will become smaller than the first or not, causing an issue:
// .substring(0, 2) and .substring(2, 0) returns the same result
// .slice(0, 2) and .slice(2, 0) doesn't return the same result
// There's also an issue with us now knowing whether the value will be negative or not, due to:
// .substring() treats a negative number the same as it treats a zero.
// The latter issue could be solved by wrapping all dynamic numbers in Math.max(0, <value>), but the resulting code would not be nice
}
}
if (sliceArguments) {
const objectText = getNodeText(objectNode);
problem.fix = fixer => fixer.replaceText(node, `${objectText}.slice(${sliceArguments.join(', ')})`);
}
context.report(problem);
}
});
};
module.exports = {
create,
meta: {
type: 'suggestion',
docs: {
url: getDocumentationUrl(__filename)
},
fixable: 'code'
}
};