add hw2

node_modules/dlv/README.md

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+# `dlv(obj, keypath)` [![NPM](https://img.shields.io/npm/v/dlv.svg)](https://npmjs.com/package/dlv) [![Build](https://travis-ci.org/developit/dlv.svg?branch=master)](https://travis-ci.org/developit/dlv)
+
+> Safely get a dot-notated path within a nested object, with ability to return a default if the full key path does not exist or the value is undefined
+
+
+### Why?
+
+Smallest possible implementation: only **130 bytes.**
+
+You could write this yourself, but then you'd have to write [tests].
+
+Supports ES Modules, CommonJS and globals.
+
+
+### Installation
+
+`npm install --save dlv`
+
+
+### Usage
+
+`delve(object, keypath, [default])`
+
+```js
+import delve from 'dlv';
+
+let obj = {
+	a: {
+		b: {
+			c: 1,
+			d: undefined,
+			e: null
+		}
+	}
+};
+
+//use string dot notation for keys
+delve(obj, 'a.b.c') === 1;
+
+//or use an array key
+delve(obj, ['a', 'b', 'c']) === 1;
+
+delve(obj, 'a.b') === obj.a.b;
+
+//returns undefined if the full key path does not exist and no default is specified
+delve(obj, 'a.b.f') === undefined;
+
+//optional third parameter for default if the full key in path is missing
+delve(obj, 'a.b.f', 'foo') === 'foo';
+
+//or if the key exists but the value is undefined
+delve(obj, 'a.b.d', 'foo') === 'foo';
+
+//Non-truthy defined values are still returned if they exist at the full keypath
+delve(obj, 'a.b.e', 'foo') === null;
+
+//undefined obj or key returns undefined, unless a default is supplied
+delve(undefined, 'a.b.c') === undefined;
+delve(undefined, 'a.b.c', 'foo') === 'foo';
+delve(obj, undefined, 'foo') === 'foo';
+```
+
+
+### Setter Counterparts
+
+- [dset](https://github.com/lukeed/dset) by [@lukeed](https://github.com/lukeed) is the spiritual "set" counterpart of `dlv` and very fast.
+- [bury](https://github.com/kalmbach/bury) by [@kalmbach](https://github.com/kalmbach) does the opposite of `dlv` and is implemented in a very similar manner.
+
+
+### License
+
+[MIT](https://oss.ninja/mit/developit/)
+
+
+[preact]: https://github.com/developit/preact
+[tests]: https://github.com/developit/dlv/blob/master/test.js