work.suroh.tk/node_modules/token-stream/index.js

31 lines
841 B
JavaScript

'use strict';
module.exports = TokenStream;
function TokenStream(tokens) {
if (!Array.isArray(tokens)) {
throw new TypeError('tokens must be passed to TokenStream as an array.');
}
this._tokens = tokens;
}
TokenStream.prototype.lookahead = function (index) {
if (this._tokens.length <= index) {
throw new Error('Cannot read past the end of a stream');
}
return this._tokens[index];
};
TokenStream.prototype.peek = function () {
if (this._tokens.length === 0) {
throw new Error('Cannot read past the end of a stream');
}
return this._tokens[0];
};
TokenStream.prototype.advance = function () {
if (this._tokens.length === 0) {
throw new Error('Cannot read past the end of a stream');
}
return this._tokens.shift();
};
TokenStream.prototype.defer = function (token) {
this._tokens.unshift(token);
};