feat: add a mechanism to retrieve all context (with defaults) (#1751)

Previously, all users of constructs would have to know beforehand the keys in the context to expect, and use either `tryGetContext` or `getContext` to retrieve a specific key from context.

This provides a mechanism to get the full context of a node in the construct tree, with overridable defaults. 

The `getAllContext` method allows users to retrieve all context. The interface for `getContext` and `tryGetContext` remains unchanged. 

I have also fixed a small typo in the library.

src/construct.ts

@@ -44,7 +44,7 @@ export class Node {
   /**
    * The id of this construct within the current scope.
    *
-   * This is a a scope-unique id. To obtain an app-unique id for this construct, use `addr`.
+   * This is a scope-unique id. To obtain an app-unique id for this construct, use `addr`.
    */
   public readonly id: string;
 
@@ -236,6 +236,25 @@ export class Node {
     return this.scope && this.scope.node.getContext(key);
   }
 
+  /**
+   * Retrieves the all context of a node from tree context.
+   *
+   * Context is usually initialized at the root, but can be overridden at any point in the tree.
+   *
+   * @param defaults Any keys to override the retrieved context
+   * @returns The context object or an empty object if there is discovered context
+   */
+  public getAllContext(defaults?: object): any {
+    if (typeof defaults === 'undefined') {
+      defaults = {};
+    }
+
+    if (this.scope === undefined) { return defaults; }
+
+    const value = { ...this._context, ...defaults };
+    return this.scope && this.scope.node.getAllContext(value);
+  }
+
   /**
    * Retrieves a value from tree context.
    *

test/construct.test.ts

@@ -150,6 +150,22 @@ test('construct.getContext(key) throws if context is not defined', () => {
   }).toThrowError(`No context value present for ${key} key`);
 });
 
+test('construct.getAllContext can be used to read the full context of a node', () => {
+  // GIVEN
+  const context = {
+    ctx1: 12,
+    ctx2: 'hello',
+  };
+
+  // WHEN
+  const t = createTree(context);
+  t.child1_1_1.node.setContext('ctx1', 13);
+
+  // THEN
+  expect(t.child1_2.node.getAllContext()).toStrictEqual(context);
+  expect(t.child1_1_1.node.getAllContext()).toStrictEqual({ ctx1: 13, ctx2: 'hello' });
+});
+
 test('construct.tryGetContext(key) can be used to read a value from context defined at the root level', () => {
   const context = {
     ctx1: 12,