name: duk_instanceof

proto: |
  duk_bool_t duk_instanceof(duk_context *ctx, duk_idx_t index1, duk_idx_t index2);

stack: |
  [ ... val1! ... val2! ... ]

summary: |
  <p>Compare values at <code>index1</code> and <code>index2</code> using the
  Ecmascript <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.8.6">instanceof</a>
  operator.  Returns 1 if <code>val1 instanceof val2</code>, 0 if not.  Throws an error
  if either index is invalid; <code>instanceof</code> itself also throws errors for
  invalid argument types.</p>

  <div class="note">
  The error throwing behavior for invalid indices differs from the behavior of
  e.g. <code>duk_equals()</code>, and matches the strictness of <code>instanceof</code>.
  For example, if rval (index2) is not a callable object <code>instanceof</code>
  throws a TypeError.  Throwing an error for an invalid index is consistent with
  instanceof strictness.
  </div>

example: |
  duk_idx_t idx_val;

  duk_get_global_string(ctx, "Error");

  if (duk_instanceof(ctx, idx_val, -1)) {
      printf("value at idx_val is an instanceof Error\n");
  }

tags:
  - compare

introduced: 1.3.0