prefer-promise-reject-errors.js
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/**
* @fileoverview restrict values that can be used as Promise rejection reasons
* @author Teddy Katz
*/
"use strict";
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "require using Error objects as Promise rejection reasons",
category: "Best Practices",
recommended: false,
url: "https://eslint.org/docs/rules/prefer-promise-reject-errors"
},
fixable: null,
schema: [
{
type: "object",
properties: {
allowEmptyReject: { type: "boolean", default: false }
},
additionalProperties: false
}
],
messages: {
rejectAnError: "Expected the Promise rejection reason to be an Error."
}
},
create(context) {
const ALLOW_EMPTY_REJECT = context.options.length && context.options[0].allowEmptyReject;
//----------------------------------------------------------------------
// Helpers
//----------------------------------------------------------------------
/**
* Checks the argument of a reject() or Promise.reject() CallExpression, and reports it if it can't be an Error
* @param {ASTNode} callExpression A CallExpression node which is used to reject a Promise
* @returns {void}
*/
function checkRejectCall(callExpression) {
if (!callExpression.arguments.length && ALLOW_EMPTY_REJECT) {
return;
}
if (
!callExpression.arguments.length ||
!astUtils.couldBeError(callExpression.arguments[0]) ||
callExpression.arguments[0].type === "Identifier" && callExpression.arguments[0].name === "undefined"
) {
context.report({
node: callExpression,
messageId: "rejectAnError"
});
}
}
/**
* Determines whether a function call is a Promise.reject() call
* @param {ASTNode} node A CallExpression node
* @returns {boolean} `true` if the call is a Promise.reject() call
*/
function isPromiseRejectCall(node) {
return astUtils.isSpecificMemberAccess(node.callee, "Promise", "reject");
}
//----------------------------------------------------------------------
// Public
//----------------------------------------------------------------------
return {
// Check `Promise.reject(value)` calls.
CallExpression(node) {
if (isPromiseRejectCall(node)) {
checkRejectCall(node);
}
},
/*
* Check for `new Promise((resolve, reject) => {})`, and check for reject() calls.
* This function is run on "NewExpression:exit" instead of "NewExpression" to ensure that
* the nodes in the expression already have the `parent` property.
*/
"NewExpression:exit"(node) {
if (
node.callee.type === "Identifier" && node.callee.name === "Promise" &&
node.arguments.length && astUtils.isFunction(node.arguments[0]) &&
node.arguments[0].params.length > 1 && node.arguments[0].params[1].type === "Identifier"
) {
context.getDeclaredVariables(node.arguments[0])
/*
* Find the first variable that matches the second parameter's name.
* If the first parameter has the same name as the second parameter, then the variable will actually
* be "declared" when the first parameter is evaluated, but then it will be immediately overwritten
* by the second parameter. It's not possible for an expression with the variable to be evaluated before
* the variable is overwritten, because functions with duplicate parameters cannot have destructuring or
* default assignments in their parameter lists. Therefore, it's not necessary to explicitly account for
* this case.
*/
.find(variable => variable.name === node.arguments[0].params[1].name)
// Get the references to that variable.
.references
// Only check the references that read the parameter's value.
.filter(ref => ref.isRead())
// Only check the references that are used as the callee in a function call, e.g. `reject(foo)`.
.filter(ref => ref.identifier.parent.type === "CallExpression" && ref.identifier === ref.identifier.parent.callee)
// Check the argument of the function call to determine whether it's an Error.
.forEach(ref => checkRejectCall(ref.identifier.parent));
}
}
};
}
};