Do we need to put "use strict" in external js files if our html file (which imports the external js files) already has "use strict" ?
And if our external js files do not have "use strict", are they still "strict" within a HTML file that has "use strict" ?
Example:
<!DOCTYPE html>
<html>
<head>
<title></title>
<script>
"use strict";
function f() {
// calling File1 functions (File1 does not have "use strict"; at the top)
// are the File1 functions "strict"?
}
</script>
<script src="File1.js"></script>
<script>
//by the way.. is it strict here ?
</script>
</head>
<body>
</body>
</html>
Do we need to put "use strict" in external js files if our html file (which imports the external js files) already has "use strict" ?
And if our external js files do not have "use strict", are they still "strict" within a HTML file that has "use strict" ?
Example:
<!DOCTYPE html>
<html>
<head>
<title></title>
<script>
"use strict";
function f() {
// calling File1 functions (File1 does not have "use strict"; at the top)
// are the File1 functions "strict"?
}
</script>
<script src="File1.js"></script>
<script>
//by the way.. is it strict here ?
</script>
</head>
<body>
</body>
</html>
- Why not? Are you worried about 15 bytes or so? – beatgammit Commented Jul 5, 2011 at 6:44
- 8 you totally misunderstood my question – Li Juan Commented Jul 5, 2011 at 6:55
- Uh, my comment was trying to probe into why you even needed to know. Put use strict everywhere to make it more portable. The 15 bytes or so isn't going to kill you, so use it for clarity's sake. – beatgammit Commented Jul 5, 2011 at 8:45
1 Answer
Reset to default 22You must put "use strict"; (or 'use strict';) at the top of each script (or function) to make them strict. In your example, the functions in File1.js will not be strict, nor will the second block. See https://developer.mozilla.org/en/JavaScript/Strict_mode#Invoking_strict_mode for details.
If this wasn't the case, using strict mode could invalidate third-party scripts that you import, so it makes sense that strictness only applies to the scripts and individual functions that you explicitly specify.
For example:
external.js:
console.log("C: This script is non-strict.");
var g = function (x) {
console.log("g is non-strict regardless of caller.");
return 2 * x;
};
test.html:
<!DOCTYPE html>
<html>
<head>
<title></title>
<script>
"use strict";
console.log("A: This script element is strict.");
function f() {
console.log("The strictness of a script does not affect" +
" the strictness of external scripts, so g is" +
" still non-strict when called from f.");
return g(3);
}
</script>
<script src="external.js"></script>
<script>
f();
console.log("B: This script element is non-strict.")
</script>
</head>
<body>
</body>
</html>