This is my solution:

function resolve(path, obj) {
    return path.split('.').reduce(function(prev, curr) {
        return prev ? prev[curr] : null
    }, obj || self)
}

Usage example:

resolve("document.body.style.width")
// 或者
resolve("style.width", document.body)
// 或者甚至使用数组索引
// （someObject已在问题中定义）
resolve("part.0.size", someObject) 
// 当中间属性未定义时返回null：
resolve('properties.that.do.not.exist', {hello:'world'})

There are two ways to access object properties: Dot notation : something.bar and square bracket notation: something['bar'].

The value in the square brackets can be any expression. Therefore, if the property name is stored in a variable, square bracket notation must be used:

var something = {
  bar: 'foo'
};
var foo = 'bar';

// both x = something[foo] and something[foo] = x work as expected
console.log(something[foo]);
console.log(something.bar)