Monthly Archives: September 2011

javascript NaN

Posted by bower on September 25, 2011
javascript / No Comments

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javascript 中有一个值NaN 它是一个怪胎

NaN 的意思是 Not a Number

但是 typeof NaN  // number 也就是说 NaN是数字类型的 ecma的文档里确实这么写的

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javascript 内部属性[[Class]]

Posted by bower on September 22, 2011
javascript / 1 Comment

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jvascript object 内部属性, 每一个对象都有这些内部属性

Internal Property Value Type Domain Description
[[Prototype]] Object or Null The prototype of this object.
[[Class]] String A String value indicating a specification defined classification of objects.
[[Extensible]] Boolean If true, own properties may be added to the object.
[[Get]] SpecOp(propertyName) →
any
Returns the value of the named property.
[[GetOwnProperty]] SpecOp (propertyName) → Undefined orProperty Descriptor Returns the Property Descriptor of the named own property of this object, orundefined if absent.
[[GetProperty]] SpecOp (propertyName) → Undefined or Property Descriptor Returns the fully populated Property Descriptor of the named property of this object, or undefined if absent.
[[Put]] SpecOp (propertyName, any, Boolean) Sets the specified named property to the value of the second parameter. The flag controls failure handling.
[[CanPut]] SpecOp (propertyName) → Boolean Returns a Boolean value indicating whether a [[Put]] operation withpropertyName can be performed.
[[HasProperty]] SpecOp (propertyName → Boolean) Returns a Boolean value indicating whether the object already has a property with the given name.
[[Delete]] SpecOp (propertyName, Boolean) → Boolean Removes the specified named own property from the object. The flag controls failure handling.
[[DefaultValue]] SpecOp (Hint) → primitive Hint is a String. Returns a default value for the object.
[[DefineOwnProperty]] SpecOp (propertyName, PropertyDescriptor, Boolean) → Boolean Creates or alters the named own property to have the state described by a Property Descriptor. The flag controls failure handling.

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css position absolute 绝对定位

Posted by bower on September 09, 2011
cross browser / No Comments

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最近面试了几个前端页面人员  发现很多人对 position 这个属性不明白, 这个出乎我的意料, 在这我就科普一下

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