Function eval_js

pywebio/session/__init__.py:358–406

Execute JavaScript expression in the user's browser and get the value of the expression :param str expression_: JavaScript expression. The value of the expression need to be JSON-serializable. If the value of the expression is a `promise <https://developer.mozilla.org/en-US/docs/Web/Java

(expression_, **args)

@chose_impl
def eval_js(expression_, **args):
    """Execute JavaScript expression in the user's browser and get the value of the expression

    :param str expression_: JavaScript expression. The value of the expression need to be JSON-serializable.
       If the value of the expression is a `promise <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise>`_,
       ``eval_js()`` will wait for the promise to resolve and return the value of it. When the promise is rejected, `None` is returned.
    :param args: Local variables passed to js code. Variables need to be JSON-serializable.
    :return: The value of the expression.

    Note: When using :ref:`coroutine-based session <coroutine_based_session>`,
    you need to use the ``await eval_js(expression)`` syntax to call the function.

    Example:

    .. exportable-codeblock::
        :name: eval_js
        :summary: `eval_js()` usage

        current_url = eval_js("window.location.href")
        put_text(current_url)  # ..demo-only

        ## ----
        function_res = eval_js(''&#x27;(function(){
            var a = 1;
            a += b;
            return a;
        })()''&#x27;, b=100)
        put_text(function_res)  # ..demo-only

        ## ----
        promise_res = eval_js(''&#x27;new Promise(resolve => {
            setTimeout(() => {
                resolve('Returned inside callback.');
            }, 2000);
        });''&#x27;)
        put_text(promise_res)  # ..demo-only

    .. versionchanged:: 1.3

       The JS expression support return promise.
    """

    from ..io_ctrl import send_msg
    send_msg('run_script', spec=dict(code=expression_, args=args, eval=True))

    res = yield next_client_event()
    assert res['event'] == 'js_yield', "Internal Error, please report this bug on " \
                                       "https://github.com/wang0618/PyWebIO/issues"
    return res['data']


@check_session_impl(CoroutineBasedSession)