From 3c4efd2e775fe60854dc08ab25c0396544fcdc51 Mon Sep 17 00:00:00 2001
From: Yulong Wang <7679871+fs-eire@users.noreply.github.com>
Date: Wed, 8 Mar 2023 15:29:04 -0800
Subject: [PATCH] [js/common] allows polyfill for bigint (#14921)

### Description
This change delays the execution of checking whether bigint is available
in the context. This allows polyfill for
`BigInt64Array`/`BigUint64Array` (if there is any)
---
 js/common/lib/tensor-impl.ts | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/js/common/lib/tensor-impl.ts b/js/common/lib/tensor-impl.ts
index 80fc150af0..81c3c0674e 100644
--- a/js/common/lib/tensor-impl.ts
+++ b/js/common/lib/tensor-impl.ts
@@ -11,9 +11,6 @@ type SupportedTypedArrayConstructors = Float32ArrayConstructor|Uint8ArrayConstru
     Float64ArrayConstructor|Uint32ArrayConstructor|BigUint64ArrayConstructor;
 type SupportedTypedArray = InstanceType<SupportedTypedArrayConstructors>;
 
-const isBigInt64ArrayAvailable = typeof BigInt64Array !== 'undefined' && typeof BigInt64Array.from === 'function';
-const isBigUint64ArrayAvailable = typeof BigUint64Array !== 'undefined' && typeof BigUint64Array.from === 'function';
-
 // a runtime map that maps type string to TypedArray constructor. Should match Tensor.DataTypeMap.
 const NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP = new Map<string, SupportedTypedArrayConstructors>([
   ['float32', Float32Array],
@@ -39,14 +36,27 @@ const NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP = new Map<SupportedTypedArrayConstru
   [Uint32Array, 'uint32'],
 ]);
 
-if (isBigInt64ArrayAvailable) {
-  NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP.set('int64', BigInt64Array);
-  NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP.set(BigInt64Array, 'int64');
-}
-if (isBigUint64ArrayAvailable) {
-  NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP.set('uint64', BigUint64Array);
-  NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP.set(BigUint64Array, 'uint64');
-}
+// the following code allows delaying execution of BigInt checking. This allows lazy initialization for
+// NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP and NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP, which allows BigInt polyfill
+// if available.
+let isBigIntChecked = false;
+const checkBigInt = () => {
+  if (!isBigIntChecked) {
+    isBigIntChecked = true;
+    const isBigInt64ArrayAvailable = typeof BigInt64Array !== 'undefined' && typeof BigInt64Array.from === 'function';
+    const isBigUint64ArrayAvailable =
+        typeof BigUint64Array !== 'undefined' && typeof BigUint64Array.from === 'function';
+
+    if (isBigInt64ArrayAvailable) {
+      NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP.set('int64', BigInt64Array);
+      NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP.set(BigInt64Array, 'int64');
+    }
+    if (isBigUint64ArrayAvailable) {
+      NUMERIC_TENSOR_TYPE_TO_TYPEDARRAY_MAP.set('uint64', BigUint64Array);
+      NUMERIC_TENSOR_TYPEDARRAY_TO_TYPE_MAP.set(BigUint64Array, 'uint64');
+    }
+  }
+};
 
 /**
  * calculate size from dims.
@@ -75,6 +85,8 @@ export class Tensor implements TensorInterface {
   constructor(
       arg0: TensorType|TensorDataType|readonly boolean[], arg1?: TensorDataType|readonly number[]|readonly boolean[],
       arg2?: readonly number[]) {
+    checkBigInt();
+
     let type: TensorType;
     let data: TensorDataType;
     let dims: typeof arg1|typeof arg2;