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Simayi( Sima yi ) Get internal variables “ Shu Kingdom ” Code for : But in the face of ah Dou, he can't help mediocrity, Can only return to heaven, Shu finally failed to unify the Three Kingdoms, On the contrary, ah Dou left a laughing stock of not thinking of Shu. Īnyone who has read the Three Kingdoms should know, Although Zhuge Liang is called Wolong. Through this code, you can see, Because Zhuge Liang is a local variable created in his own function ” Shu Kingdom ” So Sima Yi wanted to get var str3 = “ Shu Kingdom ” That would be a mistake, Come to nothing. Simayi() // Console error Sima Yi could not attack Shu however, I've already said that, Under normal circumstances, This is inaccessible.
YOU DONT KNOW JS SCOPE CLOSURE HOW TO
Two 、 How to access local variables inside a function from the outsideįor a variety of reasons, Sometimes we need to get local variables in a function. ġ、 Global variables can be read directly inside the functionĢ、 Local variables inside the function cannot be read directly outside the function There is one caveat, If not used inside the function var To declare variables, Then this variable is not a local variable, It's a global variable. So we can infer the variables declared inside the function, It's a local variable.
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Uncaught ReferenceError: str1 is not definedĮxplain this variable str1 It can only be accessed and used by its own function, When calling outside the function, due to no permission to access the function test1() The variable of, Therefore, the console reports an error “ Variable not defined ”. Since everyone has access to this variable, Then it means that the variables declared outside the function body are global variables. Įxplain this variable str Can be accessed directly outside the function, This variable can also be accessed by the function. Here are a few simple examples, Let's show the difference between global variables and local variables. The scope of a variable is nothing more than two : Global and local variables. So when talking about closures, Take a look back. Under normal circumstances, One function is “ Have no right ” Access variables in the scope of another function. My first understanding of closures comes from 《 three 》, First, just by “ Entitled ”’ Two words, we can further infer. 《JavaScript Advanced program 3rd Edition 》 # Step 3: Pause the code with a breakpointĪ common method for debugging a problem like this is to insert a lot of console.log() statements into the code, in order to inspect values as the script executes.A closure is a function that has access to variables in the scope of another function.
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If your DevTools window is wide, this pane is displayed to the right of the Code Editor pane. Various tools for inspecting the page's JavaScript. After selecting a file in the File Navigator pane, the contents of that file are displayed here. Every file that the page requests is listed here. This shortcut opens the Console panel.įigure 4. Open DevTools by pressing Command+Option+I (Mac) or Control+Shift+I (Windows, Linux). The Sources panel is where you debug JavaScript. # Step 2: Get familiar with the Sources panel UIĭevTools provides a lot of different tools for different tasks, such as changing CSS, profiling page load performance, and monitoring network requests. This is the bug you're going to fix.įigure 1. The label below the button says 5 + 1 = 51. The demo opens in a new tab.Ĭlick Add Number 1 and Number 2.
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Finding a series of actions that consistently reproduces a bug is always the first step to debugging.Ĭlick Open Demo.