解读JavaScript中 For, While与递归的用法

for循环:

for(i=start; i<end; i++) {

}

while (condition) {
     //do something;
     //change condition;
}

function substring(all, start, end) {
    for(i=start; i<=end; i++) {
         console.log(all[i]);
    }

substring("eclipse", 1, 4);   //clip

function substring(all, start, end) {
    if(start >= end) {
        return all[start];
    }
    else {
        return all[start] + substring(all, start+1, end);
    }

substring("eclipse", 1, 4);    //clip

对于数组,字符串, 我们使用index []访问特定的值; 对于对象,也是一样使用[], 但我们会使用一个特殊的变量: propertyName

var person = {
    name: "Morgan Jones",
    telephone: "(650) 777 - 7777",
    email: "morgan.jones@example.com"
};

for (var propertyName in person) {
    console.log(propertyName + ":"+ person[propertyName]);
}

var table = [
    ["Person",  "Age",  "City"],
    ["Sue",     22,     "San Francisco"],
    ["Joe",     45,     "Halifax"]
];

var i;
var rows=table.length;
for (r=0;r<rows;r++) {
    var c;
    var cells = table[r].length;
    var rowText = "";
    for (c=0;c<cells;c++) {
        rowText += table[r][c];
        if (c < cells-1) {
            rowText += "  ";
        }
    }
    console.log(rowText);
}

Sue 22 San Francisco

Joe 45 Halifax

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break:

使用break立刻退出循环, 适用于for和while循环.