simple_json_parser.ts

class JSONParser {

	static parse(json: string): any {
		var parser = new JSONParser(json);
		return parser.parseValue();
	}

	private index: number = 0;
	private ch: string;
	private text: string;

	constructor(text: string) {
		this.text = text;
		this.ch = this.text[0];
	}

	next(c?: string) {
		if (typeof c !== 'undefined' && c !== this.ch) {
			this.error("expected '" + c + "', got '" + this.ch + "'");
		}
		this.index++;
		this.ch = this.text.charAt(this.index);
	}

	error(msg: string) {
		throw new SyntaxError("SyntaxError at " + this.index + ": " + msg)
	}

	parseNumber(): number {
		var s = '';
		while ('0' <= this.ch && this.ch <= '9') {
			s += this.ch;
			this.next();
		}
		return parseFloat(s);
	}

	parseWord(): any {
		switch (this.ch) {
			case 'f':
				this.next('f');
				this.next('a');
				this.next('l');
				this.next('s');
				this.next('e');
				return false;
			case 't':
				this.next('t');
				this.next('r');
				this.next('u');
				this.next('e');
				return true;
			case 'n':
				this.next('n');
				this.next('u');
				this.next('l');
				this.next('l');
				return null;
			default:
				this.error('Invalid word');
		}
	}

	parseString(): string {
		var s = '';
		this.next('"');
		while(this.ch !== '"') {
			s += this.ch;
			this.next();
		}
		this.next('"');
		return s;
	}

	skipWhitespace(): void {
		var whitespace = ['\n', '\r', '\t', ' '];
		while (whitespace.indexOf(this.ch) !== -1) {
			this.next();
		}
	}

	parseValue(): any {
		switch (this.ch) {
			case '[':
				return this.parseArray();
			case '{':
				return this.parseObject();
			case '"':
				return this.parseString();
			default:
				if ('0' <= this.ch && this.ch <= '9') {
					return this.parseNumber();
				}
				else {
					return this.parseWord();
				}
		}
	}

	parseArray(): Array<any> {
		var array = [];
		this.next('[');
		this.skipWhitespace();
		while (this.ch !== ']') {
			if (this.ch === ',') {
				this.next(',');
			}
			else {
				array.push(this.parseValue());
			}
			this.skipWhitespace();
		}
		this.next(']');
		return array;
	}

	parseObject(): any {
		var obj = {};
		this.next('{');
		while (this.ch !== '}') {
			this.skipWhitespace();
			var key = this.parseString();
			this.skipWhitespace();
			this.next(':');
			this.skipWhitespace();
			obj[key] = this.parseValue();
			this.skipWhitespace();
			if (this.ch === ',') {
				this.next(',');
			}
			else if (this.ch !== '}') {
				this.error("Invalid Object Literal");
			}
		}
		this.next('}');
		return obj;
	}
}