Update README.md

README.md

@@ -1,2 +1,81 @@
 # TypeAssert
 Minimal JavaScript type assertions
+
+## Basic usage
+```javascript
+const { typeAssert } = require('./typeAssert')
+
+// simple types
+typeAssert(1, 'number')
+typeAssert(2, 'string')
+
+// object
+typeAssert({ x: 1, y: 3 }, 'object')
+typeAssert({ x: 1, y: 3 }, {})
+
+// array
+typeAssert([1, 2, 3], 'Array')
+typeAssert([1, 2, 3], [])
+
+// object fields
+typeAssert({
+    x: 1,
+    y: '2'
+}, {
+    x: 'number',
+    y: 'string'
+})
+
+// array elements
+typeAssert([1, 2, 3], ['number'])
+
+// "sum" types
+const assertion = 'string'.sumWith('number')
+typeAssert('abc', assertion)
+typeAssert(123, assertion)
+
+// nullable types
+const assertion = { x: 'number', y: 'function' }.orNull()
+typeAssert({
+    x: 144,
+    y: () => {}
+}, assertion)
+typeAssert(null, assertion)
+
+// nullable shorthand for simple types
+typeAssert(114, 'number?')
+typeAssert(null, 'number?)
+
+// nested situation
+const assertion = {
+    a: 'number',
+    b: 'string',
+    c: [
+        {
+            x: 'function',
+            y: 'function'
+        }.sumWith({
+            x: [],
+            y: {}
+        }).orNull()
+    ]
+}
+
+typeAssert({
+    a: 114,
+    b: '514',
+    c: [
+        null,
+        {
+            x: [1, 2, 3],
+            y: {
+                z: '4'
+            }
+        },
+        {
+            x: console.log,
+            y: Array.prototype.push
+        }
+    ]
+}, assertion)
+```