汗学院：javascript循环运行时间太长

我正在阅读可汗学院算法课程。我在https://www.khanacademy.org/computing/computer-science/algorithms/sorting-algorithms/p/challenge-find-minimum-in-subarray

代码挑战应该遍历数组查找并返回子数组中的最低编号。我写了一些我认为应该可以使用的代码，但是标题中出现了错误。为什么？

var indexOfMinimum = function(array, startIndex) {
    // Set initial values for minValue and minIndex,
    // based on the leftmost entry in the subarray:  
    var minValue = array[startIndex];
    var minIndex = startIndex;
    var i = minIndex + 1;
    for( i ; array.length ; i+1) {
        if( array[i]< minValue) {
            minIndex = i ;
            minValue = array[i];
        }
    } 

    // Loop over items starting with startIndex, 
    // updating minValue and minIndex as needed:

    return minIndex;
}; 

var array = [18, 6, 66, 44, 9, 22, 14];   
var index = indexOfMinimum(array, 2);