#2797 - Partial Function with Placeholders

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Problem Description

Given a function fn and an array args, return a function partialFn.

Placeholders "_" in the args should be replaced with values from restArgs starting from index 0. Any remaining values in the restArgs should be added at the end of the args.

partialFn should return a result of fn. fn should be called with the elements of the modified args passed as separate arguments.

Solution

/**
 * @param {Function} fn
 * @param {Array} args
 * @return {Function}
 */
var partial = function(fn, args) {
  return function(...restArgs) {
    const finalArgs = [...args];
    let restIndex = 0;

    for (let i = 0; i < finalArgs.length; i++) {
      if (finalArgs[i] === '_' && restIndex < restArgs.length) {
        finalArgs[i] = restArgs[restIndex];
        restIndex++;
      }
    }

    while (restIndex < restArgs.length) {
      finalArgs.push(restArgs[restIndex]);
      restIndex++;
    }

    return fn(...finalArgs);
  };
};