流程控制

流程控制

基本

if ... else

var shoppingDone = false;

if (shoppingDone === true) {
  var childsAllowance = 10;
} else {
  var childsAllowance = 5;
}

三元运算符

var greeting = ( isBirthday ) ? 'Happy birthday!' : 'Good morning';

switch语句

var select = document.querySelector('select');
var para = document.querySelector('p');

select.addEventListener('change', setWeather);


function setWeather() {
  var choice = select.value;

  switch (choice) {
    case 'sunny':
      para.textContent = 'sunny outside today. ';
      break;
    case 'rainy':
      para.textContent = 'Rain is falling outside;';
      break;
    case 'snowing':
      para.textContent = 'The snow is coming down ';
      break;
    case 'overcast':
      para.textContent = 'overcast.';
      break;
    default:
      para.textContent = '';
  }
}

循环

for

var cats = ['Bill', 'Jeff', 'Pete', 'Biggles', 'Jasmin'];
var info = 'My cats are called ';
var para = document.querySelector('p');

for (var i = 0; i < cats.length; i++) {
  info += cats[i] + ', ';
}

para.textContent = info;

while

var i = 0;

while (i < cats.length) {
  if (i === cats.length - 1) {
    info += 'and ' + cats[i] + '.';
  } else {
    info += cats[i] + ', ';
  }

  i++;
}