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That had the benefit of never breaking existing code. But the downside was that any mistake or an imperfect decision made by JavaScript's creators got stuck in the language forever.
ဒီလိုမျိုး လုပ်ဆောင်ချက်အဟောင်းကိုလည်း မပြောင်း၊ အသစ်တွေကိုလည်း ဒီ JavaScript Language ထဲထည့်ခြင်းက ကျတော်တို့ အရင်ကတည်းက ရေးထားတဲ့ Code တွေကိုလည်း run လို့ရနေတယ်ဗျ။ ဒါပေမဲ့ ဒီ Language ကို ရေးခဲ့တဲ့ Developer တွေရဲ့ အမှား(သို့) သိပ်မသေချာတဲ့ ယူဆချက်တွေ လုပ်မိခဲ့ရင်တော့ JavaScript Language ထဲမှာ ရှိနေတယ်ဗျ။
This was the case until 2009 whenECMAScript 5(ES5) appeared. It added new features to the language and modified some of the existing ones. To keep the old codeworking, most such modifications are off by default. You need to explicitly enable them with a special directive:`"use strict"`.
Quite soon we're going to learnfunctions(a way to group commands), so let's note in advance that`"use strict"`can be put at the beginning of afunction. Doing that enablesstrict modein that functiononly. But usually people use it for the whole script.
Modern JavaScriptsupports "classes"and "modules"- advanced language structures (we'll surely get to them),that enable `use strict` automatically. So we don't need to add the`"use strict"`directive, if we use them.
In the next chapters, as we learn language features, we'll see the differences between the strict and old modes. Luckily, there aren't many and they actually make our lives better.
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