JS: Define expression.add(…) to build new expression

packages/expressions/lib/expression.js

@@ -51,4 +51,12 @@ export class Expression {
   matches (schema) {
     return this.validate(schema).valid
   }
+
+  add (expression) {
+    if (this.schema.maxItems) {
+      return Expression.build({ All: [this, expression] })
+    } else {
+      return this.clone({ args: [...this.args, expression] })
+    }
+  }
 }

packages/expressions/test/expression.test.js

@@ -85,4 +85,21 @@ describe('Expression', () => {
       expect(expression.validate().valid).toBe(false)
     })
   })
+
+  describe('add', () => {
+    test('Any returns new expression with added arg', () => {
+      const expression = Expression.build({ Any: [] }).add(true)
+      expect(expression.value).toEqual({ Any: [true] })
+    })
+
+    test('Max returns new expression with added arg', () => {
+      const expression = Expression.build({ Max: [1] }).add(2)
+      expect(expression.value).toEqual({ Max: [1, 2] })
+    })
+
+    test('Equal returns new expression wrapped in All', () => {
+      const expression = Expression.build({ Equal: [1, 1] }).add(false)
+      expect(expression.value).toEqual({ All: [{ Equal: [1, 1] }, false] })
+    })
+  })
 })