add section on timers #1201
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add section on timers #1201
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| console.log(`My name is ${name}`); | ||
| } | ||
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| setTimeout(printMessage, 3000, "Sally"); // <-- Call printMessage after at least 3000ms |
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| setTimeout(printMessage, 3000, "Sally"); // <-- Call printMessage after at least 3000ms | |
| setTimeout(printMessage, 3000, "Sally"); // <-- Call printMessage after at least 3000ms, with the argument "Sally" |
| } | ||
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| setTimeout(printMessage, 3000, "Sally"); // <-- Call printMessage after at least 3000ms | ||
| printName("Daniel"); |
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| printName("Daniel"); | |
| printMessage("Daniel"); |
| printName("Daniel"); | ||
| ``` | ||
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| In this example, we define the function and call `printMessage` just once. However, we're also using a built-in function called `setTimeout`. `setTimeout` allows us to set a minimum amount of time after which a function will be called back. |
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| In this example, we define the function and call `printMessage` just once. However, we're also using a built-in function called `setTimeout`. `setTimeout` allows us to set a minimum amount of time after which a function will be called back. | |
| In this example, we define the function and call `printMessage` just once. We also call it ourselves once. We're also using a built-in function called `setTimeout`. `setTimeout` allows us to set a minimum amount of time after which a function will be called back. |
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| > "After at least 3000 ms, call the function `printMessage`, and when you call back `printMessage`, pass the input of `"Sally"` to `printMessage`." | ||
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| Notice we're saying _at least_ 3000 ms because `setTimeout` guarantees a minimum amount of time: it doesn't say that `printMessage` muse be called _exactly_ after 3000 ms. In this example, we say that `printMessage` is a {{<tooltip title="callback function">}}A callback function is a function that is passed as an argument to another function and gets executed after the main function has finished its execution.{{</tooltip>}} as it is _called back_ after 3000 miliseconds. In the terminal, we'll see "Daniel" appear first and then after an at least 3000 ms delay, we'll see the console log of "Sally" |
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| Notice we're saying _at least_ 3000 ms because `setTimeout` guarantees a minimum amount of time: it doesn't say that `printMessage` muse be called _exactly_ after 3000 ms. In this example, we say that `printMessage` is a {{<tooltip title="callback function">}}A callback function is a function that is passed as an argument to another function and gets executed after the main function has finished its execution.{{</tooltip>}} as it is _called back_ after 3000 miliseconds. In the terminal, we'll see "Daniel" appear first and then after an at least 3000 ms delay, we'll see the console log of "Sally" | |
| Notice we're saying _at least_ 3000 ms because `setTimeout` guarantees a minimum amount of time: it doesn't say that `printMessage` muse be called _exactly_ after 3000 ms. In this example, we say that `printMessage` is a {{<tooltip title="callback function">}}A callback function is a function that is passed as an argument to another function. We ourselves don't call the callback function - something else will call it for us at the right time.{{</tooltip>}} as it is _called back_ after 3000 miliseconds. In the terminal, we'll see "Daniel" appear first and then after an at least 3000 ms delay, we'll see the console log of "Sally". |
A callback function is more general than this... In the context of setTimeout this tooltip seems correct, but more generally "some other code" will call a callback "when it should", right? Like [1, 2, 3].map(x => x + 1) - the arrow function there is still a callback function, but it will be executed before the main function finishes. And [].map(x => x + 1) - the callback function is never actually called. But these are still callback functions.
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What does this change?
Address #1115
Common Content?
Common Theme?
Yes - it adds to the js2 section.
Issue number: #1115
Org Content?
Updates Data Groups -> Section 3 -> prep
Module | Sprint | Page Type | Block Type
Checklist
Who needs to know about this?