JavaScript: Takes a function as an argument, then makes the first argument the last

JavaScript fundamental (ES6 Syntax): Exercise-232 with Solution

Move First Argument Last

Write a JavaScript program that takes a function as an argument, then makes the first argument the last.

• Use argument destructuring and a closure with variadic arguments.
• Splice the first argument, using the spread operator (...), to make it the last before applying the rest.

Sample Solution:

JavaScript Code:

// Define a function 'flip' that takes a function 'fn' as input and returns a new function that flips the first two arguments before calling 'fn'
const flip = fn => (first, ...rest) => fn(...rest, first);

// Initialize objects 'a' and 'b'
let a = { name: 'John Smith' };
let b = {};

// Define a function 'mergeFrom' using 'flip' and 'Object.assign' that merges the properties of the second object into the first object
const mergeFrom = flip(Object.assign);

// Bind 'mergeFrom' to 'a' to create a new function 'mergePerson' that merges properties from 'a' into another object
let mergePerson = mergeFrom.bind(null, a);

// Merge properties from 'a' into 'b' using the 'mergePerson' function
mergePerson(b); // == b

// Reinitialize object 'b'
b = {};

// Log the result of merging properties from 'a' into 'b' using 'Object.assign'
console.log(Object.assign(b, a)); // == b

Output:

{"name":"John Smith"}

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-232-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that takes a function and returns a new function which moves the first argument to the end of the arguments list.
• Write a JavaScript function that rearranges its input arguments so that the first becomes the last before invoking the original function.
• Write a JavaScript program that demonstrates parameter shifting by cyclically rotating the arguments of a function.
• Write a JavaScript function that wraps another function to automatically reposition its first argument to the final slot.

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