When using BrowserCompatible, BigDecimal in the Double range behaves the same as Double. for issue #3123

core/src/main/java/com/alibaba/fastjson2/JSONWriter.java

@@ -864,8 +864,7 @@ protected static boolean isWriteAsString(BigDecimal value, long features) {
         }
 
         return (features & BrowserCompatible.mask) != 0
-                && value.precision() >= 16
-                && !isJavaScriptSupport(value.unscaledValue());
+                && !isJavaScriptSupport(value);
     }
 
     public abstract void writeNameRaw(char[] chars);

core/src/main/java/com/alibaba/fastjson2/util/TypeUtils.java

@@ -4347,8 +4347,23 @@ public static boolean isJavaScriptSupport(long i) {
         return i >= LONG_JAVASCRIPT_LOW && i <= LONG_JAVASCRIPT_HIGH;
     }
 
-    public static boolean isJavaScriptSupport(BigDecimal i) {
-        return i.precision() >= 16 && isJavaScriptSupport(i.unscaledValue());
+    public static boolean isJavaScriptSupport(BigDecimal decimal) {
+        boolean jsSupport = decimal.precision() < 16 || isJavaScriptSupport(decimal.unscaledValue());
+        if (!jsSupport && decimal.scale() != 0) {
+            //Use double for comparison
+            //double and javascript number have the same precision
+            //In extreme cases, precision loss may occur.
+            //There will be a loss of precision between [4.9e-324, 5e-324), which will be converted to 5e-324 by JavaScript.
+            //This situation can be ignored
+            double doubleValue;
+            try {
+                doubleValue = decimal.doubleValue();
+            } catch (Exception ex) {
+                return false;
+            }
+            jsSupport = decimal.compareTo(BigDecimal.valueOf(doubleValue)) == 0;
+        }
+        return jsSupport;
     }
 
     public static boolean isJavaScriptSupport(BigInteger i) {

core/src/test/java/com/alibaba/fastjson2/issues_3100/Issue3123.java

@@ -0,0 +1,44 @@
+package com.alibaba.fastjson2.issues_3100;
+
+import com.alibaba.fastjson2.JSON;
+import com.alibaba.fastjson2.JSONWriter;
+import lombok.SneakyThrows;
+import org.junit.jupiter.api.Test;
+import org.skyscreamer.jsonassert.JSONAssert;
+
+import java.math.BigDecimal;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * @author 张治保
+ * @since 2024/10/22
+ */
+public class Issue3123 {
+    @Test
+    @SneakyThrows
+    void test() {
+        BigDecimal num1 = BigDecimal.valueOf(107.29305145106407);
+        BigDecimal num2 = BigDecimal.valueOf(23.42835970945431);
+        BigDecimal num3 = BigDecimal.valueOf(23.427479896686418);
+
+        Double num11 = 107.29305145106407;
+        Double num21 = 23.42835970945431;
+        Double num31 = 23.427479896686418;
+
+        Map map = new HashMap<>();
+        map.put("b1", num1);
+        map.put("b2", num2);
+        map.put("b3", num3);
+
+        map.put("d1", num11);
+        map.put("d2", num21);
+        map.put("d3", num31);
+
+        JSONAssert.assertEquals(
+                "{\"b1\":107.29305145106407,\"b2\":23.42835970945431,\"b3\":23.427479896686418,\"d1\":107.29305145106407,\"d2\":23.42835970945431,\"d3\":23.427479896686418}",
+                JSON.toJSONString(map, JSONWriter.Feature.BrowserCompatible),
+                true
+        );
+    }
+}