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// @flow
import {Token} from "./Token";
import type {AnyParseNode} from "./parseNode";
/**
* This is the ParseError class, which is the main error thrown by KaTeX
* functions when something has gone wrong. This is used to distinguish internal
* errors from errors in the expression that the user provided.
*
* If possible, a caller should provide a Token or ParseNode with information
* about where in the source string the problem occurred.
*/
class ParseError {
name: "ParseError";
position: number | void;
// Error start position based on passed-in Token or ParseNode.
length: number | void;
// Length of affected text based on passed-in Token or ParseNode.
rawMessage: string | void;
// The underlying error message without any context added.
constructor(
message: string, // The error message
token?: ?Token | AnyParseNode, // An object providing position information
): ParseError {
let error = "KaTeX parse error: " + message;
let start;
let end;
const loc = token && token.loc;
if (loc && loc.start <= loc.end) {
// If we have the input and a position, make the error a bit fancier
// Get the input
const input = loc.lexer.input;
// Prepend some information
start = loc.start;
end = loc.end;
if (start === input.length) {
error += " at end of input: ";
} else {
error += " at position " + (start + 1) + ": ";
}
// Underline token in question using combining underscores
const underlined = input.slice(start, end).replace(/[^]/g, "$&\u0332");
// Extract some context from the input and add it to the error
let left;
if (start > 15) {
left = "…" + input.slice(start - 15, start);
} else {
left = input.slice(0, start);
}
let right;
if (end + 15 < input.length) {
right = input.slice(end, end + 15) + "…";
} else {
right = input.slice(end);
}
error += left + underlined + right;
}
// Some hackery to make ParseError a prototype of Error
// See http://stackoverflow.com/a/8460753
// $FlowFixMe
const self: ParseError = new Error(error);
self.name = "ParseError";
// $FlowFixMe
self.__proto__ = ParseError.prototype;
self.position = start;
if (start != null && end != null) {
self.length = end - start;
}
self.rawMessage = message;
return self;
}
}
// $FlowFixMe More hackery
ParseError.prototype.__proto__ = Error.prototype;
export default ParseError;
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