1. Start
Recently, I would like to write down some Javascript tips I want to keep organized while completing a Google-Apps-Script project.
2. Deployment
go straight to the content
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When you want an empty array value to evaluate to false Suppose there is a function that searches for specific files in a folder and returns the searched file names as an array (eg, an newFilesarray). At this time, if the array is empty, falsy valueyou will want the empty array to be evaluated as , so that subsequent file processing is not performed . However, unlike Python, if ( newfiles )when processing falseas , it is not judged as . If if ( newfiles.length )you want to judge according to the intention of the title , use . For a detailed explanation of the content…
- Reference book: Lee Sun Brown, Learning JavaScript, 3rd Edition (2016), Translation-Hanbit Media (2017), p151. 5.7.1 True-Equal Values and False-Equal Values
- MDN > Definitions of Web-realated terms > Fasly : false-like values Except for the above values, all values are the same (Truthy)
- MDN > Definitions of Web-realated terms > Truthy : true-like values
Truthy values to watch out for All objects, even those that return false when the valueOf( ) method is called, are also true values. All arrays, even empty arrays are true Strings with only spaces (“ “, etc.) String “false” isEven & isOdd single line function const isEven = n => n % 2 == 0 const isOdd = n => Math.abs(n % 2) == 1 When confused about the use of this in eventlistner Reference link: What is ‘this’ in event listeners? problem When this is used in the eventlistener callback function, this does not refer to the object that has the callback function as a member. At this time, the bound element of the eventlistner is used as this, so it cannot be performed as intended. solution Old fashioned solution: handleEvent Nowadays solution: bind() Another solution: arrow function For more details, see the reference link above.
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