使用reduce将数组转换为对象数组

@EDIT了GrégoryNEUT 加入交代

// Two thing to know first :

// When no initial value is provided,
// Array.reduce takes the index 0 as first value and start to loop at index 1

// Doing (x, y, z)
// Will execute the code x, y and z

// Equivalent to :

// x;
// y;
// z;

let ex = 0;

console.log((ex = 2, ex = 5, ex = 3));

// So about the code

const getParts = (a) => {
  // We are creating a new function here so we can have an array where to
  // push data to
  const func = (r) => {
    // Because there is no initial value
    //
    // Start will be the value at index 0 of the array
    // The loop is gonna start at index 1 of the array
    a.reduce((start, end) => {
      console.log(start, end);

      r.push({
        start,
        end,
      });

      return end;
    });

    return r;
  };

  return func([]);
};

// Equivalent
const getPartsEquivalent = (a) => {
  const r = [];

  // Because there is no initial value
  //
  // Start will be the value at index 0 of the array
  // The loop is gonna start at index 1 of the array
  a.reduce((start, end) => {
    console.log(start, end);

    r.push({
      start,
      end,
    });

    return end;
  });

  return r;
};

var optimizedRoute = ['Bengaluru', 'Salem', 'Erode', 'Tiruppur', 'Coimbatore']

console.log(getPartsEquivalent(optimizedRoute));

.as-console-wrapper {
  max-height: 100% !important;
  top: 0;
}

getParts = a => (                   // take a as array and return an IIFE
    r => (                          // with an initialized result array
        a.reduce((start, end) => (  // reduce array by taking two values
            r.push({ start, end }), // push short hand properties
            end                     // and take the last value as start value for next loop
        )),
        r                           // finally return result
    )
)([]);                              // call IIFE with empty array

const getParts = a => (r => (a.reduce((start, end) => (r.push({ start, end }), end)), r))([]);

var optimizedRoute = ['Bengaluru', 'Salem', 'Erode', 'Tiruppur', 'Coimbatore']

console.log(getParts(optimizedRoute));

.as-console-wrapper { max-height: 100% !important; top: 0; }

optimizedRoute = ['Bengaluru', 'Salem', 'Erode', 'Tiruppur', 'Coimbatore']
var result = optimizedRoute
                .slice(0, -1)
                .map((item, index) => ({start : item, end : optimizedRoute[index + 1]}));
console.log(result);

const optimizedRoute = ['Bengaluru', 'Salem', 'Erode', 'Tiruppur', 'Coimbatore'];
const result = new Array(optimizedRoute.length - 1);

for (let i = 0; i