h系タグからインデックスを作る

makeIndex.js

function makeIndex(get_elem_selector, set_elem_selector){
    var glem = document.querySelector(get_elem_selector)
    var slem = document.querySelector(set_elem_selector)
    if(!glem || !slem) throw "element not found"
    var hs = []
    !function recur(elem){
        var match = elem.tagName.match(/^H([1-9])$/)
        if(match){
            hs.push([+match[1], elem.textContent])
        }else{
            [].forEach.call(elem.children, recur)
        }
    }(glem)
    var etree = function(){
        var root = document.createElement("ul")
        var now_level = 1
        var ptr = root
        hs.forEach(function(e){
            var level = e[0]
            var text = e[1]
            if(now_level < level){
                level_in(level - now_level)
            }else if(now_level > level){
                level_out(now_level - level)
            }
            add_elem(text)
            now_level = level
        })
        return root
        
        function level_in(n){
            while(n--){
                // make "li" if empty "ul"
                if(!ptr.lastElementChild){
                    ptr.appendChild(document.createElement("li"))
                }
                var ul = document.createElement("ul")
                ptr.lastElementChild.appendChild(ul)
                ptr = ul
            }
        }
        function level_out(n){
            while(n--){
                ptr = ptr.parentElement.parentElement
            }
        }
        function add_elem(text){
            var li = document.createElement("li")
            li.textContent = text
            ptr.appendChild(li)
        }
    }()
    slem.appendChild(etree)
    return etree
}