import {Parser, Token, types} from 'cst';
let Property = types.ObjectProperty;
let Identifier = types.Identifier;
let code = `({a: b})`; // So called "Important line"!
let program = new Parser().parse(code);
// Now find the object
let expression = program.body[0].expression;
// Now find the "}" inside the object
let parentheses = expression.lastChild;
// Now add stuff after the "a: b"  
expression.insertChildBefore(new Token('Punctuator', ','), parentheses);
expression.insertChildBefore(new Token('Whitespace', ' '), parentheses);
// Now we have this thing - ({a: b, })
// Now a complicated bit (which will be improved in the future)...
// Now for every "Node" we need a special constructor,
// like "Property" or "Identifier".
// 
// And you need to pass array to them, since there might different length
// of tokens in them.
// 
// Punctuators or whitespaces do not have to be wrapped though -  
let prop = new Property([
    new Identifier([new Token('Identifier', 'c')]),
    new Token('Punctuator', ':'),
    new Token('Whitespace', ' '),
    new Identifier([new Token('Identifier', 'd')]),
]);
expression.insertChildBefore(prop, parentheses);
console.log(program.getSourceCode()); // now - ({a: b, c: d})