JSON Pointer [RFC6901](http://tools.ietf.org/html/rfc6901) sample implementation.

JSONPointer.js

function parseJSONPointer(string) {
    if (string.length < 1) {
        return []; // root
    }
    
    if (string[0] !== '/') {
        throw new Error('Invalid JSON Pointer syntax');
    }
    
    return string.split('/').map(function(referenceToken){
        return referenceToken.replace(/~./, function(escaped) {
            switch (escaped) {
                case '~0':
                    return '~';
                case '~1':
                    return '/';
            }
            
            throw new Error('Invalid JSON Pointer syntax');
        })
    }).slice(1);
}

function getByJSONPointer(target, pointer) {

    function get (target, pointerArray) {
        if (pointerArray.length === 0) {
            return target;
        }
        
        if ( target instanceof Array && pointerArray[0] != parseInt(pointerArray[0]) || target[pointerArray[0]] === undefined) {
            thorw new Error('Pointer references a nonexistent value');
        }
        
        return get(target[pointerArray[0]], pointerArray.splice(1));
    }
    
    return get(target, parseJSONPointer(pointer));
}

function setByJSONPointer(target, pointer, value) {
    
    if (pointer === '') {
        // pointerが自身を指してるときどうしよう......
        // 自身に代入でもしてもらおうか
        return value;
    }
    
    function set (target, pointerArray, value) {
        if (pointerArray.length > 1) {

            if ( target instanceof Array && pointerArray[0] != parseInt(pointerArray[0]) || target[pointerArray[0]] === undefined) {
                thorw new Error('Pointer references a nonexistent value');
            }

            return set(target[pointerArray[0]], pointerArray.splice(1));
        }

        var key = pointerArray[0];
        if ( target instanceof Array ) {
            if (key === '-') {
                target.push(value);

                return;
            }
            
            if (key != parseInt(key)) {
                thorw new Error('Pointer references a nonexistent value');
            }
        }

        target[key] = value;
    }

    set(target, parseJSONPointer(pointer));

    return target;
}

refs RFC6901