for Statement

The for class of statements should have the following form:

for (initialization; condition; update) {
    statements
}

for (variable in object) {
    statements
}

Variables should not be declared in the initialization section of a for statement.

// Good
var i,
    len;

for (i=0, len=10; i < len; i++) {
    // code
}

// Bad: Variables declared during initialization
for (var i=0, len=10; i < len; i++) {
    // code
}

// Bad: Variables declared during initialization
for (var prop in object) {
    // code
}

When using a for-in statement, double-check if you need to use hasOwnProperty() to filter out object members.