Does anyone know the significance of the square brackets preceding the method call in this code snippet? It's a new syntax for me...
return [].concat(privateUserList);Appreciate any insights!
Does anyone know the significance of the square brackets preceding the method call in this code snippet? It's a new syntax for me...
return [].concat(privateUserList);Appreciate any insights!
In programming, an [] represents an empty array, while [1,2,3,4] would be an array containing four elements.
This code snippet initializes an empty array and then appends the privateUserList to it.
[] is used to create an empty array. When [].concat is called, it takes the privateUserList and creates a new array with the same entries as the original array. If privateUserList is not an array, the new array will contain just the privateUserList itself.
Some may argue that this method is theoretically inefficient because it generates and discards an array (since concat creates a new array, the original empty array created by [] is thrown away). However, similar idioms that involve creating and discarding arrays are common and tend to be optimized.
If we assume that privateUserList is an array, a more direct way to achieve the same result is:
return privateUserList.slice();
If we need to support anything that is array-like (which concat does not), we can use:
return Array.prototype.slice.call(privateUserList);
Alternatively, in ES2015 (or with a shim), we can use:
return Array.from(privateUserList);
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