Enhance all functions to have the callPolyfill method. The method accepts an object obj as its first parameter and any number of additional arguments. The obj becomes the this context for the function. The additional arguments are passed to the function (that the callPolyfill method belongs on).
For example if you had the function:
function tax(price, taxRate) {
const totalCost = price * (1 + taxRate);
console.log(`The cost of ${this.item} is ${totalCost}`);
}
Calling this function like tax(10, 0.1) will log "The cost of undefined is 11". This is because the this context was not defined.
However, calling the function like tax.callPolyfill({item: "salad"}, 10, 0.1) will log "The cost of salad is 11". The this context was appropriately set, and the function logged an appropriate output.
Please solve this without using the built-in Function.call method.
Example 1:
Input:
fn = function add(b) {
return this.a + b;
}
args = [{"a": 5}, 7]
Output: 12
Explanation:
fn.callPolyfill({"a": 5}, 7); // 12
callPolyfill sets the "this" context to {"a": 5}. 7 is passed as an argument.
Example 2:
Input:
fn = function tax(price, taxRate) {
return `The cost of the ${this.item} is ${price * taxRate}`;
}
args = [{"item": "burger"}, 10, 1.1]
Output: "The cost of the burger is 11"
Explanation: callPolyfill sets the "this" context to {"item": "burger"}. 10 and 1.1 are passed as additional arguments.
Constraints:
typeof args[0] == 'object' and args[0] != null1 <= args.length <= 1002 <= JSON.stringify(args[0]).length <= 105The key idea in #2693 Call Function with Custom Context is understanding how JavaScript handles the this keyword. Functions can be executed with a specific object as their context using built-in mechanisms like call, apply, or bind. The goal is to wrap an existing function so that when it executes, the this value points to the provided object.
A common approach is to return a new function that forwards all received arguments to the original function while explicitly setting the context. This can be done by invoking the original function with the supplied object as its context. The wrapper simply captures the arguments and delegates execution.
This technique effectively simulates how function context manipulation works internally in JavaScript. Since the operation only forwards arguments and invokes the function, it runs in constant time and requires constant extra space.
| Approach | Time Complexity | Space Complexity |
|---|---|---|
| Wrapper Function with Custom Context | O(1) | O(1) |
NeetCode
The first approach involves augmenting the Function prototype to add our custom callPolyfill method. This method should simulate the behavior of the native Function.prototype.call method. We'll save the original context of this, invoke our function with the given context, and apply the additional arguments.
Time Complexity: O(1) — The time to set a property and invoke a function is constant.
Space Complexity: O(1) — Space used is constant because no structures grow with input size.
1Function.prototype.callPolyfill = function(obj, ...args) {
2 const uniqueID = Symbol('context');
3 obj[uniqueID] = this;
4 const result = obj[uniqueID](...args);
5 delete obj[uniqueID];
6 return result;
7};In this solution, we temporarily assign the function to be called as a property of the context object using a symbol to avoid potential property name clashes. We then call the function using this set context and pass the function arguments using the spread operator. After calling the function, we delete the temporary property to clean up.
This approach leverages closures to encapsulate the function call logic. By using an immediately invoked function expression (IIFE), we can create a local scope that captures the context and arguments for the function call.
Time Complexity: O(1) — Function invocation is a constant time operation.
Space Complexity: O(1) — No additional space is required.
1Function.prototype.callPolyfill = function(obj,Watch expert explanations and walkthroughs
Jot down your thoughts, approach, and key learnings
This problem mainly tests understanding of the JavaScript this keyword and function context binding. It also evaluates knowledge of higher-order functions and how arguments can be forwarded from one function to another.
Questions involving function context, closures, and higher-order functions are common in JavaScript interviews at top tech companies. While the exact problem may vary, the concepts behind this question are frequently tested.
No specific data structure is required for this problem. The focus is on function wrapping and context binding rather than storing or processing data structures.
The optimal approach is to return a wrapper function that invokes the original function while explicitly setting its context. This is typically done using JavaScript mechanisms like call, apply, or bind so that the provided object becomes the value of this during execution.
This solution wraps the call to this.apply within an arrow function, effectively using a closure to capture the current function, context, and arguments. The function is immediately invoked to simulate a direct call.