آموزش جاوا اسکریپت Java Script قسمت چهارم

 <div id="demo">0</div>

<input type="button" value="start" />

<input type="button" value="stop" />

 <script src="Scripts/script.js"></script>

 "use strict";
x = 3.14; // This will cause an error (if x has not been declared)
//*******************************
"use strict";
x = 3.14;
delete x; // This will cause an error
//***************************
"use strict";
var x = {p1:10, p1:20}; // This will cause an error
//***************************

"use strict";
function x(p1, p1) {}; // This will cause an error

 setTimeout(function(){ alert("Hello"); }, 3000);

 setInterval(function(){ alert("Hello"); }, 3000);

 'use strict';
var s = 0;
setInterval(function () { document.getElementById("demo").innerText = ++s; }, 1000);

 var s = 2;

s = s + 1;

alert(s);

//**************

alert(s++); // alert(2)

//*************

alert(++s); // alert(3)

 document.querySelector("p");
document.querySelector(".example");
document.querySelector("p.example");
document.querySelector("#demo");
document.querySelector("div > p");
document.querySelector("a[target]");
document.querySelector("a[target=’_blank’]");
document.querySelector("h2, h3");

 'use strict';
var s = 0;
setInterval(function () { document.querySelector("#demo").innerText = ++s; }, 1000);

 <input type="button" value="start" onclick="setInterval(function () { document.querySelector('#demo').innerText = ++s; }, 1000);" />
'use strict';
var s = 0;

 function myFunction(param1, param2) {
 // body of function
}

 'use strict';
var s = 0;
function showTime() {
 setInterval(function () { document.querySelector("#demo").innerText = ++s; }, 1000);
}
<input type="button" value="start" onclick="showTime()" />