[tfjs-layers] Fix a silent error in L1/L2/L1L2 regularizer constructor (

#1861)

Re. #1773

BUG

Previosly, if you pass a number argument to `tf.regularizers.l2()`,
for example, no error will be thrown, even though the specified number
will not take effect as the regularization coefficient.

This PR fixes that by explicitly checking the type of the arg.

tfjs-layers/src/regularizers.ts

@@ -15,6 +15,14 @@ import {abs, add, Scalar, serialization, sum, Tensor, tidy, zeros} from '@tensor
 import * as K from './backend/tfjs_backend';
 import {deserializeKerasObject, serializeKerasObject} from './utils/generic_utils';
 
+function assertObjectArgs(args: L1Args | L2Args | L1L2Args): void {
+  if (args != null && typeof args !== 'object') {
+    throw new Error(
+        `Argument to L1L2 regularizer's constructor is expected to be an ` +
+        `object, but received: ${args}`);
+  }
+}
+
 /**
  * Regularizer base class.
  */
@@ -50,6 +58,8 @@ export class L1L2 extends Regularizer {
   constructor(args?: L1L2Args) {
     super();
 
+    assertObjectArgs(args);
+
     this.l1 = args == null || args.l1 == null ? 0.01 : args.l1;
     this.l2 = args == null || args.l2 == null ? 0.01 : args.l2;
     this.hasL1 = this.l1 !== 0;
@@ -88,10 +98,12 @@ export class L1L2 extends Regularizer {
 serialization.registerClass(L1L2);
 
 export function l1(args?: L1Args) {
+  assertObjectArgs(args);
   return new L1L2({l1: args != null ? args.l1 : null, l2: 0});
 }
 
 export function l2(args: L2Args) {
+  assertObjectArgs(args);
   return new L1L2({l2: args != null ? args.l2 : null, l1: 0});
 }
 

tfjs-layers/src/regularizers_test.ts

@@ -44,6 +44,17 @@ describeMathCPU('Built-in Regularizers', () => {
     expectTensorsClose(
         score, scalar(1 * (1 + 2 + 3 + 4) + 2 * (1 + 4 + 9 + 16)));
   });
+  it('Using number arg for constructor leads to error', () => {
+    // tslint:disable-next-line:no-any
+    expect(() => tfl.regularizers.l1(0.001 as any))
+        .toThrowError(/expected.*object.*received.*0\.001/);
+    // tslint:disable-next-line:no-any
+    expect(() => tfl.regularizers.l2(0.001 as any))
+        .toThrowError(/expected.*object.*received.*0\.001/);
+        // tslint:disable-next-line:no-any
+    expect(() => tfl.regularizers.l1l2(0.001 as any))
+        .toThrowError(/expected.*object.*received.*0\.001/);
+  });
 });
 
 describeMathCPU('regularizers.get', () => {