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The second – press Enter on an input field. Both actions lead to submit event on the form.… In the form below: Go into the text field and press Enter.… Both actions show alert and the form is not sent anywhere due to return false:… Relation between submit and click When a form is sent using Enter

body alert(i) Runs again and again while the condition is truthy.… Namely, alert.… So the alert is only called for odd values.… But as a side effect, this created one more level of nesting (the alert call inside the curly braces)… So the control goes straight from (*) to alert('Done!').

Losing the focus generally means: “the data has been entered”, so we can run the code to check it or… In the example below: The blur handler checks if the field has an email entered, and if not – shows… If we enter something into the input and then try to use Tab or click away from the <input>, then… But also JavaScript itself may cause it, for instance: An alert moves focus to itself, so it causes… the focus loss at the element (blur event), and when the alert is dismissed, the focus comes back (focus

For example, alert automatically converts any value to a string to show it.… For example, alert(value) does it to show the value.… required when we read a value from a string-based source like a text form but expect a number to be entered

We can type commands there and press Enter to execute.… If we click it now, alert will be shown.… Step” command, but behaves differently if the next statement is a function call (not a built-in, like alert… That’s handy when we accidentally entered a nested call using , but it does not interest us, and we want

functions will be: prompt(question, [default]) Ask a question, and return either what the visitor entered… The choice is returned as true/false. alert(message) Output a message.… More in: Interaction: alert

, ""); if (n < 0) { alert(`Power ${n} is not supported, please enter a non-negative integer number… `); } else { alert( pow(x, n) ); } ``` --> Now let’s discuss the rules and reasons for them in detail

An errorless example: shows alert (1) and (2):… You can check by running the code with entering… And then enter -1 – there will be an immediate error, and the execution will take 0ms.

using the browser as our demo environment, let’s see a couple of functions to interact with the user: alert… Summary.We covered 3 browser-specific functions to interact with visitors: alert

By the way, if we ever want to know which elements are compared – nothing prevents us from alerting them… We are writing a messaging app, and the person enters the comma-delimited list of receivers: John, Pete

Press Enter to run them. Now we can see errors, and that’s enough for a start.… Multi-line input Usually, when we put a line of code into the console, and then press Enter… To insert multiple lines, press Shift+Enter.… This way one can enter long fragments of JavaScript code.

intermediate elements may be ignored, but one thing we know for sure: if the pointer “officially” entered… They trigger when the mouse pointer enters/leaves the element.… When the pointer enters an element – mouseenter triggers.… Imagine we want to handle mouse enter/leave for table cells. And there are hundreds of cells.… Handlers for mouseenter/leave on <table> only trigger when the pointer enters/leaves the table

Once we enter strict mode, there’s no going back.… First, you can try to press Shift+Enter to input multiple lines, and put use strict on top, like this

In the example above we’ll see sequential execution of three alerts… For 0, 1, the first alert… For 2 the second alert runs.

We’ve already seen a statement, alert('Hello, world!'), which shows the message “Hello, world!”.… For example, here we split “Hello World” into two alerts:… Now let’s remove the semicolon after the alert:… We need to put a semicolon after alert for the code to work correctly.

As we can see from alert… Time goes on while alert… In most browsers, including Chrome and Firefox the internal timer continues “ticking” while showing alert… So if you run the code above and don’t dismiss the alert window for some time, then the next alert will… The actual interval between alerts will be shorter than 2 seconds.

Special keys are coded by their names: "Enter", "Backspace", "Tab" etc.… Even though we have the key filter, one still can enter anything using a mouse and right-click + Paste… Mobile devices provide other means to enter values. So the filter is not 100% reliable.

What happens when objects are added obj1 + obj2, subtracted obj1 - obj2 or printed using alert(obj)?… As for the string conversion – it usually happens when we output an object with alert(obj) and in similar… object-to-string conversion, when we’re doing an operation on an object that expects a string, like alert… So if we try to use an object as a string, like in an alert… There are 3 types (hints) of it: "string" (for alert and other operations that need a string

That is: where a Windows user presses Ctrl+Enter or Ctrl+A, a Mac user would press Cmd+Enter or Cmd+A

The focusing is still possible if we use another way to enter the input.… – checks/unchecks the input. submit – clicking an <input type="submit"> or hitting Enter

As the result is passed along the chain of handlers, we can see a sequence of alert calls: 1 → 2 → 4.… So in the code above all alert show the same: 1.… the output is the same as in the previous example: 1 → 2 → 4, but now with 1 second delay between alert

If that is also falsy, it shows the last alert. There can be more else if blocks.… gets executed and shows an alert. We don’t assign a result to a variable here.

That method runs and returns a new string (shown by alert).… Objects are always truthy in if, so here the alert

The functions alert… language (e.g. tags) and also the BOM (browser object model) – various browser functions: setTimeout, alert

Here, after if finishes, the alert… -- ```js let phrase = "Hello"; function say(name) { alert( `${phrase}, ${name}` );… In this example the search proceeds as follows: For the name variable, the alert inside say finds it… When it pauses, in the console type alert(value).

We’ve already seen examples of built-in functions, like alert(message), prompt(message, default) and… In the code above, if checkAge(age) returns false, then showMovie won’t proceed to the alert… A few examples of breaking this rule: getAge – would be bad if it shows an alert with the age (should

For instance, we can alert almost any value, and it will work. Symbols are special.… For instance, this alert will show an error:

…But if we try to store user-provided keys in it (for instance, a user-entered dictionary), we can see

Here we can see a variable sayHi getting a value, the new function, created as function() { alert… We can even print out that value using alert:

If you run it, the alert… Now the alert

And if there was an <input> with a text entered by the visitor, then the text will be removed.… Let’s say we have an arbitrary string, for instance entered by a user, and want to show it.

projects such functions have many useful features like sending logs over the network, here we’ll just use alert

The result of typeof alert is "function", because alert is a function.

forget that the code is inside the attribute and use double quotes inside, like this: onclick="alert… possible because when the browser reads the attribute, it creates a handler like this: function(event) { alert

We’ll keep the amount of browser-specific commands (like alert) to a minimum so that you don’t spend

In both examples above, alert runs without an error, because the variable phrase exists.

So, the alert shows 2.… So, the alert shows 1.

What’s interesting is that in both cases: new Animal() and new Rabbit(), the alert in the line (*) shows… And in the code above it actually works as intended: we have the correct alert.

validateEmail(email) could (besides checking the email for correctness) show an error message and ask to re-enter

So, if a visitor enters "apple", bag will become {apple: 5}.

In the first line, the OR || operator stops the evaluation immediately upon seeing true, so the alert

If we used this.name instead of user.name inside the alert

So the alerts in the example above actually display garbage.

document.documentElement: For instance, this button shows the height of your window: alert

Then, when alert tries to read property rabbit.eats (**), it’s not in rabbit, so JavaScript follows the

So, in the example below the first alert shows null:

and timeouts on this iframe --> Depending on your browser, the iframe above is either empty or alerting

So if we click on <p>, then we’ll see 3 alerts: p → div → form.

So alert shows zero sizes. At first sight, the DOMContentLoaded event is very simple.

Here’s the context stack when we entered the subcall pow(2, 2): Context: { x: 2, n: 2, at line