w3resource

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:

flowchart: Create a function that invokes fn with partials prepended to the arguments it receives

Live Demo:

See the Pen javascript-basic-exercise-170-1 by w3resource (@w3resource) on CodePen.


Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to create a function that invokes fn with partials appended to the arguments it receives.
Next: Write a JavaScript program to parse an HTTP Cookie header string and return an object of all cookie name-value pairs.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.



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