feat: optimize atobPolyfill performance to avoid minor gc

Author: Chanran

base64.js

@@ -197,17 +197,24 @@
         if (!b64re.test(asc))
             throw new TypeError('malformed base64.');
         asc += '=='.slice(2 - (asc.length & 3));
-        var u24, bin = '', r1, r2;
+        var u24, r1, r2;
+        var binArray = []; // use array to avoid minor gc in loop
         for (var i = 0; i < asc.length;) {
             u24 = b64tab[asc.charAt(i++)] << 18
                 | b64tab[asc.charAt(i++)] << 12
                 | (r1 = b64tab[asc.charAt(i++)]) << 6
                 | (r2 = b64tab[asc.charAt(i++)]);
-            bin += r1 === 64 ? _fromCC(u24 >> 16 & 255)
-                : r2 === 64 ? _fromCC(u24 >> 16 & 255, u24 >> 8 & 255)
-                    : _fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255);
+            if (r1 === 64) {
+                binArray.push(_fromCC(u24 >> 16 & 255));
+            }
+            else if (r2 === 64) {
+                binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255));
+            }
+            else {
+                binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255));
+            }
         }
-        return bin;
+        return binArray.join('');
     };
     /**
      * does what `window.atob` of web browsers do.

base64.mjs

@@ -163,17 +163,24 @@ const atobPolyfill = (asc) => {
     if (!b64re.test(asc))
         throw new TypeError('malformed base64.');
     asc += '=='.slice(2 - (asc.length & 3));
-    let u24, bin = '', r1, r2;
+    let u24, r1, r2;
+    let binArray = []; // use array to avoid minor gc in loop
     for (let i = 0; i < asc.length;) {
         u24 = b64tab[asc.charAt(i++)] << 18
             | b64tab[asc.charAt(i++)] << 12
             | (r1 = b64tab[asc.charAt(i++)]) << 6
             | (r2 = b64tab[asc.charAt(i++)]);
-        bin += r1 === 64 ? _fromCC(u24 >> 16 & 255)
-            : r2 === 64 ? _fromCC(u24 >> 16 & 255, u24 >> 8 & 255)
-                : _fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255);
+        if (r1 === 64) {
+            binArray.push(_fromCC(u24 >> 16 & 255));
+        }
+        else if (r2 === 64) {
+            binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255));
+        }
+        else {
+            binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255));
+        }
     }
-    return bin;
+    return binArray.join('');
 };
 /**
  * does what `window.atob` of web browsers do.

base64.ts

@@ -169,17 +169,22 @@ const atobPolyfill = (asc: string) => {
     asc = asc.replace(/\s+/g, '');
     if (!b64re.test(asc)) throw new TypeError('malformed base64.');
     asc += '=='.slice(2 - (asc.length & 3));
-    let u24, bin = '', r1, r2;
+    let u24, r1, r2;
+    let binArray: string[] = []; // use array to avoid minor gc in loop
     for (let i = 0; i < asc.length;) {
         u24 = b64tab[asc.charAt(i++)] << 18
             | b64tab[asc.charAt(i++)] << 12
             | (r1 = b64tab[asc.charAt(i++)]) << 6
             | (r2 = b64tab[asc.charAt(i++)]);
-        bin += r1 === 64 ? _fromCC(u24 >> 16 & 255)
-            : r2 === 64 ? _fromCC(u24 >> 16 & 255, u24 >> 8 & 255)
-                : _fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255);
+        if (r1 === 64) {
+            binArray.push(_fromCC(u24 >> 16 & 255));
+        } else if (r2 === 64) {
+            binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255));
+        } else {
+            binArray.push(_fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255));
+        }
     }
-    return bin;
+    return binArray.join('');
 };
 /**
  * does what `window.atob` of web browsers do.