Using JavaScript's Array.splice with assigning the replacements item as an array I've got to delete / replace elements in an array.
For accomplishing these task one usually uses Array.splice(). 

Problem: Array.splice() expects the replacement items as a comma separated list. But I got the values as an array. I've made this 
helper function which makes it possible to use splice with an array instead of single values. 

    // Deletes elements in an array and 
    // replaces the elements with other
    // values. 
    // -- Parameter -------------------
    // 1. Array - The array from which 
    // elements shall be deleted.
    // 2. Number - The index at which to
    // start the deletion.
    // 3. Number - The count of elements
    // to delete.
    // 4. Array - The elements to insert
    // into the target array.
    // -- Return ----------------------
    // Array - The deleted elements.

    function replaceArrayElements(
                                   targetArray,
                                   startIndex,
                                   deleteCount, 
                                   replacements ) {
    // 1. Parameter of .apply():
    //   Defining the context (this-keyword).
    // 2. Parameter: 
    //   a.) Start with the element startIndex.
    //   b.) Delete 3 elements.
    //   c.) Put these elements into the array
    //   as new values.
    //   a.), b.), c.) concated together
    //   into one array. The array is then
    //   used as the parameters of .splice().
    return Array.prototype.splice.apply(
                 targetArray, 
                 [startIndex, deleteCount].concat(replacements));
    }

    // -------- TEST ---------------------------------
    var test = [];

    for (var i = 1; i &lt;= 10; i++) {
      test.push(i);
    }

    console.log('Before insert: %o', test);

    var ret = 
      replaceArrayElements(test, 5, 3, ['Six', 'Seven', 'Eight']);

    console.log('After insert: %o', test);
    console.log('Return: %o', ret);
    // -- RESULTS -----
    // Before insert: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    // After insert: [1, 2, 3, 4, 5, "Six", "Seven", "Eight", 9, 10]
    // Return: [6, 7, 8]


The function does as expected. 
But anyway: If someone knows a better way to accomplish the task then please let me know. The same for improvement suggestions.
This looks straightforward and solid under ES5. I have no comments or criticism for that.

However, under ES6, there's the spread operator (which is relatively well supported in most modern browsers, and in Babel), with which you can effectively oneline the whole thing like so:

targetArray.splice(start, end, ...replacements);