The complete grammar must be parsed to buildParser
as a string, e.g.
PEG = require('pegjs');
var parser = PEG.buildParser(
'start\n' +
' = additive\n' +
'\n' +
'additive\n' +
' = left:multiplicative "+" right:additive { return left + right; }\n' +
' / multiplicative\n' +
'\n' +
'multiplicative\n' +
' = left:primary "*" right:multiplicative { return left * right; }\n' +
' / primary\n' +
'\n' +
'primary\n' +
' = integer\n' +
' / "(" additive:additive ")" { return additive; }\n' +
'\n' +
'integer "integer"\n' +
' = digits:[0-9]+ { return parseInt(digits.join(""), 10); }'
);
console.log(parser.parse('(1+2)*3'));