JavaScript での使用を避けるべきいくつかの関数とステートメントを要約します。

function addMethod(object, property, code) { 
object[property] = new Function(code); 
} 
addMethod(myObj, 'methodName', 'this.localVar=foo');

function addMethod(object, property, func) { 
object[property] = func; 
} 
addMethod(myObj, 'methodName', function () { 'this.localVar=foo'; });

with (test.object) { 
foo = 'Value of foo property of object'; 
bar = 'Value of bar property of object'; 
}

var myObj = test.object; 
myObj.foo = 'Value of foo property of object'; 
myObj.bar = 'Value of bar property of object';

var object = ['foo', 'bar'], i; 
for (i = 0; i < object.length; i++) { 
try { 
// do something that throws an exception 
} catch (e) { 
// handle exception 
} 
}

var object = ['foo', 'bar'], i; 
try { 
for (i = 0; i < object.length; i++) { 
// do something 
} 
} catch (e) { 
// handle exception 
}

var i, 
str = ''; 
function globalScope() { 
for (i=0; i < 100; i++) { 
str += i; // here we reference i and str in global scope which is slow 
} 
} 
globalScope();

function localScope() { 
var i, 
str = ''; 
for (i=0; i < 100; i++) { 
str += i; // i and str in local scope which is faster 
} 
} 
localScope();

var sum = 0; 
for (var i in arr) { 
sum += arr[i]; 
}

var sum = 0; 
for (var i = 0, len = arr.length; i < len; i++) { 
sum += arr[i]; 
}