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Command Line API Reference

The Command Line API contains a collection of convenience functions for performing common tasks: selecting and inspecting DOM elements, displaying data in readable format, stopping and starting the profiler, and monitoring DOM events.

$_

$_ returns the value of the most recently evaluated expression.

In the following example, a simple expression (2 + 2) is evaluated. The $_ property is then evaluated, which contains the same value:

$_ is the most recently evaluated expression

In the next example, the evaluated expression initially contains an array of names. Evaluating $_.length to find the length of the array, the value stored in $_ changes to become the latest evaluated expression, 4:

$_ changes when new commands are evaluated

$0 - $4

The $0, $1, $2, $3 and $4 commands work as a historical reference to the last five DOM elements inspected within the Elements panel or the last five JavaScript heap objects selected in the Profiles panel. $0 returns the most recently selected element or JavaScript object, $1 returns the second most recently selected one, and so on.

In the following example, an element with the class medium is selected in the Elements panel. In the Console drawer, $0 has been evaluated and displays the same element:

Example of $0

The image below shows a different element selected in the same page. The $0 now refers to newly selected element, while $1 returns the previously selected one:

Example of $1

$(selector)

$(selector) returns the reference to the first DOM element with the specified CSS selector. This function is an alias for the document.querySelector() function.

The following example returns a reference to the first <img> element in the document:

Example of $('img')

Right-click on the returned result and select 'Reveal in Elements Panel' to find it in the DOM, or 'Scroll in to View' to show it on the page.

The following example returns a reference to the currently selected element and displays its src property:

Example of $('img').src

$$(selector)

$$(selector) returns an array of elements that match the given CSS selector. This command is equivalent to calling document.querySelectorAll().

The following example uses $$() to create an array of all <img> elements in the current document and displays the value of each element's src property:

    var images = $$('img');
    for (each in images) {
        console.log(images[each].src);
    }

Example of using $$() to select all images in the document and display their
sources.

$x(path)

$x(path) returns an array of DOM elements that match the given XPath expression.

For example, the following returns all the <p> elements on the page:

    $x("//p")

Example of using an XPath selector

The following example returns all the <p> elements that contain <a> elements:

    $x("//p[a]")

Example of using a more complicated XPath selector

clear()

clear() clears the console of its history.

    clear();

copy(object)

copy(object) copies a string representation of the specified object to the clipboard.

    copy($0);

debug(function)

When the specified function is called, the debugger is invoked and breaks inside the function on the Sources panel allowing to step through the code and debug it.

    debug(getData);

Breaking inside a function with debug()

Use undebug(fn) to stop breaking on the function, or use the UI to disable all breakpoints.

For more information on breakpoints, see Pause Your Code With Breakpoints.

dir(object)

dir(object) displays an object-style listing of all the specified object's properties. This method is an alias for the Console API's console.dir() method.

The following example shows the difference between evaluating document.body directly in the command line, and using dir() to display the same element:

    document.body;
    dir(document.body);

Logging document.body with and without dir() function

For more information, see the console.dir() entry in the Console API.

dirxml(object)

dirxml(object) prints an XML representation of the specified object, as seen in the Elements tab. This method is equivalent to the console.dirxml() method.

inspect(object/function)

inspect(object/function) opens and selects the specified element or object in the appropriate panel: either the Elements panel for DOM elements or the Profiles panel for JavaScript heap objects.

The following example opens the document.body in the Elements panel:

    inspect(document.body);

Inspecting an element with inspect()

When passing a function to inspect, the function opens the document up in the Sources panel for you to inspect.

getEventListeners(object)

getEventListeners(object) returns the event listeners registered on the specified object. The return value is an object that contains an array for each registered event type ("click" or "keydown", for example). The members of each array are objects that describe the listener registered for each type. For example, the following lists all the event listeners registered on the document object:

    getEventListeners(document);

Output of using getEventListeners()

If more than one listener is registered on the specified object, then the array contains a member for each listener. In the following example, there are two event listeners registered on the #scrollingList element for the "mousedown" event:

Multiple listeners

You can further expand each of these objects to explore their properties:

Expanded view of listener object

keys(object)

keys(object) returns an array containing the names of the properties belonging to the specified object. To get the associated values of the same properties, use values().

For example, suppose your application defined the following object:

    var player1 = { "name": "Ted", "level": 42 }

Assuming player1 was defined in the global namespace (for simplicity), typing keys(player1) and values(player1) in the console results in the following:

Example of keys() and values() methods

monitor(function)

When the function specified is called, a message is logged to the console that indicates the function name along with the arguments that are passed to the function when it was called.

    function sum(x, y) {
        return x + y;
    }
    monitor(sum);

Example of monitor() method

Use unmonitor(function) to cease monitoring.

monitorEvents(object[, events])

When one of the specified events occurs on the specified object, the Event object is logged to the console. You can specify a single event to monitor, an array of events, or one of the generic events "types" mapped to a predefined collection of events. See examples below.

The following monitors all resize events on the window object.

    monitorEvents(window, "resize");

Monitoring window resize events

The following defines an array to monitor both "resize" and "scroll" events on the window object:

    monitorEvents(window, ["resize", "scroll"])

You can also specify one of the available event "types", strings that map to predefined sets of events. The table below lists the available event types and their associated event mappings:

Event type & Corresponding mapped events
mouse "mousedown", "mouseup", "click", "dblclick", "mousemove", "mouseover", "mouseout", "mousewheel"
key "keydown", "keyup", "keypress", "textInput"
touch "touchstart", "touchmove", "touchend", "touchcancel"
control "resize", "scroll", "zoom", "focus", "blur", "select", "change", "submit", "reset"

For example, the following uses the "key" event type all corresponding key events on an input text field currently selected in the Elements panel.

    monitorEvents($0, "key");

Below is sample output after typing a characters in the text field:

Monitoring key events

profile([name]) and profileEnd([name])

profile() starts a JavaScript CPU profiling session with an optional name. profileEnd() completes the profile and displays the results in the Profile panel. (See also Speed Up JavaScript Execution.)

To start profiling:

    profile("My profile")

To stop profiling and display the results in the Profiles panel:

    profileEnd("My profile")

Profiles can also be nested. For example, this will work in any order:

    profile('A');
    profile('B');
    profileEnd('A');
    profileEnd('B');

Result in the profiles panel:

Grouped profiles

table(data[, columns])

Log object data with table formatting by passing in a data object in with optional column headings. For example, to display a list of names using a table in the console, you would do:

    var names = {
        0: { firstName: "John", lastName: "Smith" },
        1: { firstName: "Jane", lastName: "Doe" }
    };
    table(names);

Example of table() method

undebug(function)

undebug(function) stops the debugging of the specified function so that when the function is called, the debugger is no longer invoked.

    undebug(getData);

unmonitor(function)

unmonitor(function) stops the monitoring of the specified function. This is used in concert with monitor(fn).

    unmonitor(getData);

unmonitorEvents(object[, events])

unmonitorEvents(object[, events]) stops monitoring events for the specified object and events. For example, the following stops all event monitoring on the window object:

    unmonitorEvents(window);

You can also selectively stop monitoring specific events on an object. For example, the following code starts monitoring all mouse events on the currently selected element, and then stops monitoring "mousemove" events (perhaps to reduce noise in the console output):

    monitorEvents($0, "mouse");
    unmonitorEvents($0, "mousemove");

values(object)

values(object) returns an array containing the values of all properties belonging to the specified object.

    values(object);