Using continuations. The function call itself and the local scope wrapped up into it can be varying degrees of expensive. When little state, because it’s inline or nearby for example, it might be optimized down to near what a for loop does. But if there’s a function call at all once it’s executed, that alone is slower than the for loop. Remember it’s a function call per element. If the function is further away with more scope, it can be more expensive both memory wise and time wise.

BTW, it's easy to test the basic primitives. I use Chrome snippets.

    test = (name, fn) => {
      const timeLimitMs = 1000
      let start = Date.now(), count = 0
      while (Date.now() - start < timeLimitMs) { fn(); count++ }
      console.log(name, count)  
    }
    var N = 1000000
    let a = new Array(N)
    test('for loop', _=> { for (var i = 0; i < N; i++) a[i] = i })
    test('map',      _=> { a = a.map((x,i) => i) })
    test('forEach',  _=> { a.forEach((v,i,a) => a[i] = i) })


    for loop 941
    map 37
    forEach 69

This is on my Mac in Chrome. So forEach is faster than map, but for loop is more than 10x faster than forEach. That's for loops with trivial work, of course. If the inside of the loop is expensive, the loop/map ratio will be lower.