LibJS: Add Number.isSafeInteger()

3 files changed, 45 insertions, 3 deletions

diff --git a/Libraries/LibJS/Runtime/NumberConstructor.cpp b/Libraries/LibJS/Runtime/NumberConstructor.cpp
index 21b6cc01ee..aeb0282514 100644
--- a/Libraries/LibJS/Runtime/NumberConstructor.cpp
+++ b/Libraries/LibJS/Runtime/NumberConstructor.cpp
@@ -30,15 +30,21 @@
 #include <LibJS/Runtime/NumberObject.h>
 #include <math.h>
 
+#define EPSILON pow(2, -52)
+#define MAX_SAFE_INTEGER pow(2, 53) - 1
+#define MIN_SAFE_INTEGER -(pow(2, 53) - 1)
+
 namespace JS {
 
 NumberConstructor::NumberConstructor()
 {
+    put_native_function("isSafeInteger", is_safe_integer, 1);
+
     put("prototype", interpreter().number_prototype());
     put("length", Value(1));
-    put("EPSILON", Value(pow(2, -52)));
-    put("MAX_SAFE_INTEGER", Value(pow(2, 53) - 1));
-    put("MIN_SAFE_INTEGER", Value(-(pow(2, 53) - 1)));
+    put("EPSILON", Value(EPSILON));
+    put("MAX_SAFE_INTEGER", Value(MAX_SAFE_INTEGER));
+    put("MIN_SAFE_INTEGER", Value(MIN_SAFE_INTEGER));
     put("NEGATIVE_INFINITY", Value(-js_infinity().as_double()));
     put("POSITIVE_INFINITY", js_infinity());
     put("NaN", js_nan());
@@ -65,4 +71,12 @@ Value NumberConstructor::construct(Interpreter& interpreter)
     return Value(interpreter.heap().allocate<NumberObject>(number));
 }
 
+Value NumberConstructor::is_safe_integer(Interpreter& interpreter)
+{
+    if (!interpreter.argument(0).is_number())
+        return Value(false);
+    auto value = interpreter.argument(0).to_number().as_double();
+    return Value((int64_t)value == value && value >= MIN_SAFE_INTEGER && value <= MAX_SAFE_INTEGER);
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/NumberConstructor.h b/Libraries/LibJS/Runtime/NumberConstructor.h
index 31bf3052a0..34d7b5d4ed 100644
--- a/Libraries/LibJS/Runtime/NumberConstructor.h
+++ b/Libraries/LibJS/Runtime/NumberConstructor.h
@@ -41,6 +41,8 @@ public:
 private:
     virtual bool has_constructor() const override { return true; }
     virtual const char* class_name() const override { return "NumberConstructor"; }
+
+    static Value is_safe_integer(Interpreter&);
 };
 
 }
diff --git a/Libraries/LibJS/Tests/Number.isSafeInteger.js b/Libraries/LibJS/Tests/Number.isSafeInteger.js
new file mode 100644
index 0000000000..ee7e2308e7
--- /dev/null
+++ b/Libraries/LibJS/Tests/Number.isSafeInteger.js
@@ -0,0 +1,26 @@
+try {
+    assert(Number.isSafeInteger.length === 1);
+    assert(Number.isSafeInteger(0) === true);
+    assert(Number.isSafeInteger(1) === true);
+    assert(Number.isSafeInteger(2.0) === true);
+    assert(Number.isSafeInteger(42) === true);
+    assert(Number.isSafeInteger(Number.MAX_SAFE_INTEGER) === true);
+    assert(Number.isSafeInteger(Number.MIN_SAFE_INTEGER) === true);
+    assert(Number.isSafeInteger() === false);
+    assert(Number.isSafeInteger("1") === false);
+    assert(Number.isSafeInteger(2.1) === false);
+    assert(Number.isSafeInteger(42.42) === false);
+    assert(Number.isSafeInteger("") === false);
+    assert(Number.isSafeInteger([]) === false);
+    assert(Number.isSafeInteger(null) === false);
+    assert(Number.isSafeInteger(undefined) === false);
+    assert(Number.isSafeInteger(NaN) === false);
+    assert(Number.isSafeInteger(Infinity) === false);
+    assert(Number.isSafeInteger(-Infinity) === false);
+    assert(Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1) === false);
+    assert(Number.isSafeInteger(Number.MIN_SAFE_INTEGER - 1) === false);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e.message);
+}