JavaScript: Create a function that invokes fn with partials prepended to the arguments it receives
JavaScript fundamental (ES6 Syntax): Exercise-170 with Solution
Write a JavaScript program to create a function that invokes fn with partials prepended to the arguments it receives.
- Use the spread operator (...) to prepend partials to the list of arguments of fn.
Sample Solution:
JavaScript Code:
//#Source https://bit.ly/2neWfJ2
const partial = (fn, ...partials) => (...args) => fn(...partials, ...args);
const greet = (greeting, name) => greeting + ' ' + name + '!';
const greetHello = partial(greet, 'Hello');
console.log(greetHello('John'));
Sample Output:
Hello John!
Flowchart:

Live Demo:
See the Pen javascript-basic-exercise-170-1 by w3resource (@w3resource) on CodePen.
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JavaScript: Tips of the Day
Checking if a key exists in a JavaScript object?
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?
var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists!
You should instead use the in operator:
"key" in obj // true, regardless of the actual value
If you want to check if a key doesn't exist, remember to use parenthesis:
!("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj"
Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:
obj.hasOwnProperty("key") // true
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists! You should instead use the in operator: "key" in obj // true, regardless of the actual value If you want to check if a key doesn't exist, remember to use parenthesis: !("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj" Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty: obj.hasOwnProperty("key") // true For performance comparison between the methods that are in, hasOwnProperty and key is undefined.
Ref: https://bit.ly/2CFNp1X
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